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 $31.82   13.275%   $36.0441   $36.04   $36.05   $36.00  
  Purchase #2 $159.38   13.647%   $181.1306   $181.13   $181.15   $181.10  
  Purchase #3 $201.40   4.742%   $210.9504   $210.95   $210.95   $211.00  
  Purchase #4 $186.29   12.126%   $208.8795   $208.88   $208.90   $208.90  
  Purchase #5 $64.87   8.330%   $70.2737   $70.27   $70.25   $70.30  
  Purchase #6 $35.31   11.281%   $39.2933   $39.29   $39.30   $39.30  
  Purchase #7 $35.35   11.309%   $39.3477   $39.35   $39.35   $39.30  
  7 purchase totals = $714.42       $785.9193   $785.91   $785.95   $785.90