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 $226.62   8.182%   $245.162   $245.16   $245.15   $245.20  
  Purchase #2 $15.53   4.484%   $16.2264   $16.23   $16.25   $16.20  
  Purchase #3 $81.85   12.337%   $91.9478   $91.95   $91.95   $91.90  
  Purchase #4 $244.66   5.478%   $258.0625   $258.06   $258.05   $258.10  
  Purchase #5 $245.85   6.645%   $262.1867   $262.19   $262.20   $262.20  
  Purchase #6 $55.43   9.431%   $60.6576   $60.66   $60.65   $60.70  
  Purchase #7 $202.99   4.498%   $212.1205   $212.12   $212.10   $212.10  
  7 purchase totals = $1,072.93       $1,146.3635   $1,146.37   $1,146.35   $1,146.40