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 $68.41   11.159%   $76.0439   $76.04   $76.05   $76.00  
  Purchase #2 $115.26   3.807%   $119.6479   $119.65   $119.65   $119.60  
  Purchase #3 $140.36   6.279%   $149.1732   $149.17   $149.15   $149.20  
  Purchase #4 $55.38   5.213%   $58.267   $58.27   $58.25   $58.30  
  Purchase #5 $143.95   12.854%   $162.4533   $162.45   $162.45   $162.50  
  Purchase #6 $58.97   12.455%   $66.3147   $66.31   $66.30   $66.30  
  Purchase #7 $69.80   13.755%   $79.401   $79.40   $79.40   $79.40  
  7 purchase totals = $652.13       $711.3010   $711.29   $711.25   $711.30