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 $87.63   8.228%   $94.8402   $94.84   $94.85   $94.80  
  Purchase #2 $86.49   7.123%   $92.6507   $92.65   $92.65   $92.70  
  Purchase #3 $25.66   11.777%   $28.682   $28.68   $28.70   $28.70  
  Purchase #4 $200.90   10.270%   $221.5324   $221.53   $221.55   $221.50  
  Purchase #5 $36.90   7.788%   $39.7738   $39.77   $39.75   $39.80  
  Purchase #6 $177.63   11.420%   $197.9153   $197.92   $197.90   $197.90  
  Purchase #7 $48.52   12.775%   $54.7184   $54.72   $54.70   $54.70  
  7 purchase totals = $663.73       $730.1128   $730.11   $730.10   $730.10