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 $62.27   6.298%   $66.1918   $66.19   $66.20   $66.20  
  Purchase #2 $115.35   12.240%   $129.4688   $129.47   $129.45   $129.50  
  Purchase #3 $41.25   10.240%   $45.474   $45.47   $45.45   $45.50  
  Purchase #4 $177.31   12.160%   $198.8709   $198.87   $198.85   $198.90  
  Purchase #5 $158.44   7.568%   $170.4307   $170.43   $170.45   $170.40  
  Purchase #6 $169.92   7.368%   $182.4397   $182.44   $182.45   $182.40  
  Purchase #7 $166.75   5.282%   $175.5577   $175.56   $175.55   $175.60  
  7 purchase totals = $891.29       $968.4336   $968.43   $968.40   $968.50