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 $83.31   13.345%   $94.4277   $94.43   $94.45   $94.40  
  Purchase #2 $74.89   6.279%   $79.5923   $79.59   $79.60   $79.60  
  Purchase #3 $64.96   12.344%   $72.9787   $72.98   $73.00   $73.00  
  Purchase #4 $81.28   9.591%   $89.0756   $89.08   $89.10   $89.10  
  Purchase #5 $65.46   7.807%   $70.5705   $70.57   $70.55   $70.60  
  Purchase #6 $214.54   13.732%   $244.0006   $244.00   $244.00   $244.00  
  Purchase #7 $73.41   3.554%   $76.019   $76.02   $76.00   $76.00  
  7 purchase totals = $657.85       $726.6644   $726.67   $726.70   $726.70