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 $140.31   9.494%   $153.631   $153.63   $153.65   $153.60  
  Purchase #2 $111.35   13.252%   $126.1061   $126.11   $126.10   $126.10  
  Purchase #3 $209.96   3.334%   $216.9601   $216.96   $216.95   $217.00  
  Purchase #4 $130.60   12.791%   $147.305   $147.31   $147.30   $147.30  
  Purchase #5 $62.77   6.218%   $66.673   $66.67   $66.65   $66.70  
  Purchase #6 $21.88   13.652%   $24.8671   $24.87   $24.85   $24.90  
  Purchase #7 $245.64   8.857%   $267.3963   $267.40   $267.40   $267.40  
  7 purchase totals = $922.51       $1,002.9386   $1,002.95   $1,002.90   $1,003.00