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 $203.86   4.292%   $212.6097   $212.61   $212.60   $212.60  
  Purchase #2 $244.81   12.521%   $275.4627   $275.46   $275.45   $275.50  
  Purchase #3 $40.51   9.579%   $44.3905   $44.39   $44.40   $44.40  
  Purchase #4 $212.80   11.141%   $236.508   $236.51   $236.50   $236.50  
  Purchase #5 $198.87   8.556%   $215.8853   $215.89   $215.90   $215.90  
  Purchase #6 $228.58   5.566%   $241.3028   $241.30   $241.30   $241.30  
  Purchase #7 $201.51   12.105%   $225.9028   $225.90   $225.90   $225.90  
  7 purchase totals = $1,330.94       $1,452.0618   $1,452.06   $1,452.05   $1,452.10