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 $10.77   3.637%   $11.1617   $11.16   $11.15   $11.20  
  Purchase #2 $233.45   8.403%   $253.0668   $253.07   $253.05   $253.10  
  Purchase #3 $33.57   3.647%   $34.7943   $34.79   $34.80   $34.80  
  Purchase #4 $236.72   11.799%   $264.6506   $264.65   $264.65   $264.70  
  Purchase #5 $53.49   5.824%   $56.6053   $56.61   $56.60   $56.60  
  Purchase #6 $178.78   12.836%   $201.7282   $201.73   $201.75   $201.70  
  Purchase #7 $236.34   4.722%   $247.5   $247.50   $247.50   $247.50  
  7 purchase totals = $983.12       $1,069.5069   $1,069.51   $1,069.50   $1,069.60