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 $9.31   9.550%   $10.1991   $10.20   $10.20   $10.20  
  Purchase #2 $170.89   6.740%   $182.408   $182.41   $182.40   $182.40  
  Purchase #3 $163.69   9.768%   $179.6792   $179.68   $179.70   $179.70  
  Purchase #4 $226.47   4.717%   $237.1526   $237.15   $237.15   $237.20  
  Purchase #5 $219.54   5.697%   $232.0472   $232.05   $232.05   $232.00  
  Purchase #6 $234.95   8.277%   $254.3968   $254.40   $254.40   $254.40  
  Purchase #7 $215.57   12.674%   $242.8913   $242.89   $242.90   $242.90  
  7 purchase totals = $1,240.42       $1,338.7742   $1,338.78   $1,338.80   $1,338.80