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 $57.80   8.872%   $62.928   $62.93   $62.95   $62.90  
  Purchase #2 $116.65   13.215%   $132.0653   $132.07   $132.05   $132.10  
  Purchase #3 $139.25   7.628%   $149.872   $149.87   $149.85   $149.90  
  Purchase #4 $241.66   13.362%   $273.9506   $273.95   $273.95   $274.00  
  Purchase #5 $109.46   4.408%   $114.285   $114.29   $114.30   $114.30  
  Purchase #6 $66.42   8.421%   $72.0132   $72.01   $72.00   $72.00  
  Purchase #7 $104.79   6.402%   $111.4987   $111.50   $111.50   $111.50  
  7 purchase totals = $836.03       $916.6128   $916.62   $916.60   $916.70