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 $200.90   3.810%   $208.5543   $208.55   $208.55   $208.60  
  Purchase #2 $220.75   5.244%   $232.3261   $232.33   $232.35   $232.30  
  Purchase #3 $129.45   5.653%   $136.7678   $136.77   $136.75   $136.80  
  Purchase #4 $65.32   7.337%   $70.1125   $70.11   $70.10   $70.10  
  Purchase #5 $180.91   4.704%   $189.42   $189.42   $189.40   $189.40  
  Purchase #6 $112.86   11.275%   $125.585   $125.59   $125.60   $125.60  
  Purchase #7 $37.51   4.448%   $39.1784   $39.18   $39.20   $39.20  
  7 purchase totals = $947.70       $1,001.9441   $1,001.95   $1,001.95   $1,002.00