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 $26.68   9.566%   $29.2322   $29.23   $29.25   $29.20  
  Purchase #2 $46.25   5.254%   $48.68   $48.68   $48.70   $48.70  
  Purchase #3 $159.92   3.552%   $165.6004   $165.60   $165.60   $165.60  
  Purchase #4 $212.81   5.389%   $224.2783   $224.28   $224.30   $224.30  
  Purchase #5 $53.82   10.610%   $59.5303   $59.53   $59.55   $59.50  
  Purchase #6 $242.26   9.550%   $265.3958   $265.40   $265.40   $265.40  
  Purchase #7 $216.48   6.343%   $230.2113   $230.21   $230.20   $230.20  
  7 purchase totals = $958.22       $1,022.9283   $1,022.93   $1,023.00   $1,022.90