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 $84.69   9.330%   $92.5916   $92.59   $92.60   $92.60  
  Purchase #2 $64.98   6.720%   $69.3467   $69.35   $69.35   $69.30  
  Purchase #3 $97.42   10.787%   $107.9287   $107.93   $107.95   $107.90  
  Purchase #4 $166.30   9.825%   $182.639   $182.64   $182.65   $182.60  
  Purchase #5 $41.39   8.858%   $45.0563   $45.06   $45.05   $45.10  
  Purchase #6 $199.51   4.874%   $209.2341   $209.23   $209.25   $209.20  
  Purchase #7 $61.45   6.533%   $65.4645   $65.46   $65.45   $65.50  
  7 purchase totals = $715.74       $772.2609   $772.26   $772.30   $772.20