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 $66.95   13.413%   $75.93   $75.93   $75.95   $75.90  
  Purchase #2 $118.65   8.543%   $128.7863   $128.79   $128.80   $128.80  
  Purchase #3 $78.53   6.837%   $83.8991   $83.90   $83.90   $83.90  
  Purchase #4 $124.40   12.288%   $139.6863   $139.69   $139.70   $139.70  
  Purchase #5 $99.77   13.701%   $113.4395   $113.44   $113.45   $113.40  
  Purchase #6 $62.46   13.628%   $70.972   $70.97   $70.95   $71.00  
  Purchase #7 $193.58   4.659%   $202.5989   $202.60   $202.60   $202.60  
  7 purchase totals = $744.34       $815.3121   $815.32   $815.35   $815.30