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 $237.30   8.588%   $257.6793   $257.68   $257.70   $257.70  
  Purchase #2 $44.41   6.560%   $47.3233   $47.32   $47.30   $47.30  
  Purchase #3 $189.99   9.301%   $207.661   $207.66   $207.65   $207.70  
  Purchase #4 $47.27   9.435%   $51.7299   $51.73   $51.75   $51.70  
  Purchase #5 $232.72   3.655%   $241.2259   $241.23   $241.25   $241.20  
  Purchase #6 $48.74   9.319%   $53.2821   $53.28   $53.30   $53.30  
  Purchase #7 $167.79   13.291%   $190.091   $190.09   $190.10   $190.10  
  7 purchase totals = $968.22       $1,048.9925   $1,048.99   $1,049.05   $1,049.00