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 $88.54   4.130%   $92.1967   $92.20   $92.20   $92.20  
  Purchase #2 $65.81   11.262%   $73.2215   $73.22   $73.20   $73.20  
  Purchase #3 $104.97   7.443%   $112.7829   $112.78   $112.80   $112.80  
  Purchase #4 $221.53   3.653%   $229.6225   $229.62   $229.60   $229.60  
  Purchase #5 $177.65   5.109%   $186.7261   $186.73   $186.75   $186.70  
  Purchase #6 $35.73   13.401%   $40.5182   $40.52   $40.50   $40.50  
  Purchase #7 $209.91   5.400%   $221.2451   $221.25   $221.25   $221.20  
  7 purchase totals = $904.14       $956.3130   $956.32   $956.30   $956.20