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 $9.91   13.540%   $11.2518   $11.25   $11.25   $11.30  
  Purchase #2 $231.58   6.756%   $247.2255   $247.23   $247.25   $247.20  
  Purchase #3 $174.36   9.746%   $191.3531   $191.35   $191.35   $191.40  
  Purchase #4 $246.95   13.298%   $279.7894   $279.79   $279.80   $279.80  
  Purchase #5 $10.98   5.385%   $11.5713   $11.57   $11.55   $11.60  
  Purchase #6 $94.34   7.207%   $101.1391   $101.14   $101.15   $101.10  
  Purchase #7 $11.32   8.613%   $12.295   $12.30   $12.30   $12.30  
  7 purchase totals = $779.44       $854.6252   $854.63   $854.65   $854.70