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 $246.79   3.344%   $255.0427   $255.04   $255.05   $255.00  
  Purchase #2 $222.58   5.506%   $234.8353   $234.84   $234.85   $234.80  
  Purchase #3 $41.79   12.447%   $46.9916   $46.99   $47.00   $47.00  
  Purchase #4 $41.34   5.208%   $43.493   $43.49   $43.50   $43.50  
  Purchase #5 $202.26   10.299%   $223.0908   $223.09   $223.10   $223.10  
  Purchase #6 $154.81   5.355%   $163.1001   $163.10   $163.10   $163.10  
  Purchase #7 $213.98   10.124%   $235.6433   $235.64   $235.65   $235.60  
  7 purchase totals = $1,123.55       $1,202.1968   $1,202.19   $1,202.25   $1,202.10