Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $211.75   8.421%   $229.5815   $229.58   $229.60   $229.60  
  Purchase #2 $162.66   7.184%   $174.3455   $174.35   $174.35   $174.30  
  Purchase #3 $216.47   13.778%   $246.2952   $246.30   $246.30   $246.30  
  Purchase #4 $114.53   11.331%   $127.5074   $127.51   $127.50   $127.50  
  Purchase #5 $175.34   13.508%   $199.0249   $199.02   $199.00   $199.00  
  Purchase #6 $146.85   4.435%   $153.3628   $153.36   $153.35   $153.40  
  Purchase #7 $201.80   10.106%   $222.1939   $222.19   $222.20   $222.20  
  7 purchase totals = $1,229.40       $1,352.3112   $1,352.31   $1,352.30   $1,352.30