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 $73.59   7.104%   $78.8178   $78.82   $78.80   $78.80  
  Purchase #2 $215.47   9.383%   $235.6876   $235.69   $235.70   $235.70  
  Purchase #3 $148.86   6.610%   $158.6996   $158.70   $158.70   $158.70  
  Purchase #4 $144.27   10.620%   $159.5915   $159.59   $159.60   $159.60  
  Purchase #5 $162.57   4.699%   $170.2092   $170.21   $170.20   $170.20  
  Purchase #6 $248.82   7.656%   $267.8697   $267.87   $267.85   $267.90  
  Purchase #7 $203.61   6.145%   $216.1218   $216.12   $216.10   $216.10  
  7 purchase totals = $1,197.19       $1,286.9972   $1,287.00   $1,286.95   $1,287.00