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 $195.54   3.111%   $201.6232   $201.62   $201.60   $201.60  
  Purchase #2 $126.52   6.428%   $134.6527   $134.65   $134.65   $134.70  
  Purchase #3 $8.56   10.700%   $9.4759   $9.48   $9.50   $9.50  
  Purchase #4 $86.77   12.775%   $97.8549   $97.85   $97.85   $97.90  
  Purchase #5 $58.33   11.391%   $64.9744   $64.97   $64.95   $65.00  
  Purchase #6 $20.69   6.227%   $21.9784   $21.98   $22.00   $22.00  
  Purchase #7 $81.28   5.499%   $85.7496   $85.75   $85.75   $85.70  
  7 purchase totals = $577.69       $616.3091   $616.30   $616.30   $616.40