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 $207.62   13.157%   $234.9366   $234.94   $234.95   $234.90  
  Purchase #2 $155.37   9.830%   $170.6429   $170.64   $170.65   $170.60  
  Purchase #3 $197.78   10.615%   $218.7743   $218.77   $218.75   $218.80  
  Purchase #4 $88.50   8.571%   $96.0853   $96.09   $96.10   $96.10  
  Purchase #5 $206.94   10.864%   $229.422   $229.42   $229.40   $229.40  
  Purchase #6 $139.71   8.241%   $151.2235   $151.22   $151.20   $151.20  
  Purchase #7 $157.91   8.559%   $171.4255   $171.43   $171.45   $171.40  
  7 purchase totals = $1,153.83       $1,272.5101   $1,272.51   $1,272.50   $1,272.40