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 $104.56   8.347%   $113.2876   $113.29   $113.30   $113.30  
  Purchase #2 $20.95   7.828%   $22.59   $22.59   $22.60   $22.60  
  Purchase #3 $117.71   5.808%   $124.5466   $124.55   $124.55   $124.50  
  Purchase #4 $120.97   4.123%   $125.9576   $125.96   $125.95   $126.00  
  Purchase #5 $187.65   12.279%   $210.6915   $210.69   $210.70   $210.70  
  Purchase #6 $146.26   13.591%   $166.1382   $166.14   $166.15   $166.10  
  Purchase #7 $244.61   6.322%   $260.0742   $260.07   $260.05   $260.10  
  7 purchase totals = $942.71       $1,023.2857   $1,023.29   $1,023.30   $1,023.30