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 $146.60   3.812%   $152.1884   $152.19   $152.20   $152.20  
  Purchase #2 $125.87   10.746%   $139.396   $139.40   $139.40   $139.40  
  Purchase #3 $67.29   8.476%   $72.9935   $72.99   $73.00   $73.00  
  Purchase #4 $110.92   9.413%   $121.3609   $121.36   $121.35   $121.40  
  Purchase #5 $146.35   5.345%   $154.1724   $154.17   $154.15   $154.20  
  Purchase #6 $6.50   5.675%   $6.8689   $6.87   $6.85   $6.90  
  Purchase #7 $155.55   13.361%   $176.333   $176.33   $176.35   $176.30  
  7 purchase totals = $759.08       $823.3131   $823.31   $823.30   $823.40