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 $31.86   5.541%   $33.6254   $33.63   $33.65   $33.60  
  Purchase #2 $183.42   7.307%   $196.8225   $196.82   $196.80   $196.80  
  Purchase #3 $148.41   6.513%   $158.0759   $158.08   $158.10   $158.10  
  Purchase #4 $236.72   13.281%   $268.1588   $268.16   $268.15   $268.20  
  Purchase #5 $151.62   11.604%   $169.214   $169.21   $169.20   $169.20  
  Purchase #6 $173.33   8.847%   $188.6645   $188.66   $188.65   $188.70  
  Purchase #7 $123.57   11.776%   $138.1216   $138.12   $138.10   $138.10  
  7 purchase totals = $1,048.93       $1,152.6827   $1,152.68   $1,152.65   $1,152.70