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 $50.38   12.871%   $56.8644   $56.86   $56.85   $56.90  
  Purchase #2 $195.57   8.374%   $211.947   $211.95   $211.95   $211.90  
  Purchase #3 $63.58   9.292%   $69.4879   $69.49   $69.50   $69.50  
  Purchase #4 $77.58   9.380%   $84.857   $84.86   $84.85   $84.90  
  Purchase #5 $82.95   13.608%   $94.2378   $94.24   $94.25   $94.20  
  Purchase #6 $191.49   9.295%   $209.289   $209.29   $209.30   $209.30  
  Purchase #7 $143.71   8.450%   $155.8535   $155.85   $155.85   $155.90  
  7 purchase totals = $805.26       $882.5366   $882.54   $882.55   $882.60