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 $92.55   5.242%   $97.4015   $97.40   $97.40   $97.40  
  Purchase #2 $188.65   3.761%   $195.7451   $195.75   $195.75   $195.70  
  Purchase #3 $196.54   4.783%   $205.9405   $205.94   $205.95   $205.90  
  Purchase #4 $21.94   11.252%   $24.4087   $24.41   $24.40   $24.40  
  Purchase #5 $104.31   5.821%   $110.3819   $110.38   $110.40   $110.40  
  Purchase #6 $31.50   6.245%   $33.4672   $33.47   $33.45   $33.50  
  Purchase #7 $14.92   8.218%   $16.1461   $16.15   $16.15   $16.10  
  7 purchase totals = $650.41       $683.4910   $683.50   $683.50   $683.40