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 $94.85   7.284%   $101.7589   $101.76   $101.75   $101.80  
  Purchase #2 $30.98   10.106%   $34.1108   $34.11   $34.10   $34.10  
  Purchase #3 $182.48   7.304%   $195.8083   $195.81   $195.80   $195.80  
  Purchase #4 $51.48   3.424%   $53.2427   $53.24   $53.25   $53.20  
  Purchase #5 $146.75   6.396%   $156.1361   $156.14   $156.15   $156.10  
  Purchase #6 $244.53   9.197%   $267.0194   $267.02   $267.00   $267.00  
  Purchase #7 $250.95   10.870%   $278.2283   $278.23   $278.25   $278.20  
  7 purchase totals = $1,002.02       $1,086.3045   $1,086.31   $1,086.30   $1,086.20