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 $75.76   13.193%   $85.755   $85.76   $85.75   $85.80  
  Purchase #2 $72.74   8.525%   $78.9411   $78.94   $78.95   $78.90  
  Purchase #3 $207.37   8.371%   $224.7289   $224.73   $224.75   $224.70  
  Purchase #4 $136.57   5.409%   $143.9571   $143.96   $143.95   $144.00  
  Purchase #5 $197.61   10.623%   $218.6021   $218.60   $218.60   $218.60  
  Purchase #6 $237.81   7.805%   $256.3711   $256.37   $256.35   $256.40  
  Purchase #7 $133.97   8.457%   $145.2998   $145.30   $145.30   $145.30  
  7 purchase totals = $1,061.83       $1,153.6551   $1,153.66   $1,153.65   $1,153.70