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 $32.47   4.213%   $33.838   $33.84   $33.85   $33.80  
  Purchase #2 $191.60   8.429%   $207.75   $207.75   $207.75   $207.80  
  Purchase #3 $136.92   11.111%   $152.1332   $152.13   $152.15   $152.10  
  Purchase #4 $146.48   5.809%   $154.989   $154.99   $155.00   $155.00  
  Purchase #5 $162.76   11.197%   $180.9842   $180.98   $181.00   $181.00  
  Purchase #6 $203.54   9.776%   $223.4381   $223.44   $223.45   $223.40  
  Purchase #7 $11.92   9.130%   $13.0083   $13.01   $13.00   $13.00  
  7 purchase totals = $885.69       $966.1408   $966.14   $966.20   $966.10