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 $228.51   11.593%   $255.0012   $255.00   $255.00   $255.00  
  Purchase #2 $86.44   8.377%   $93.6811   $93.68   $93.70   $93.70  
  Purchase #3 $110.66   5.470%   $116.7131   $116.71   $116.70   $116.70  
  Purchase #4 $137.79   5.777%   $145.7501   $145.75   $145.75   $145.80  
  Purchase #5 $138.64   9.415%   $151.693   $151.69   $151.70   $151.70  
  Purchase #6 $176.92   3.422%   $182.9742   $182.97   $182.95   $183.00  
  Purchase #7 $222.71   8.543%   $241.7361   $241.74   $241.75   $241.70  
  7 purchase totals = $1,101.67       $1,187.5488   $1,187.54   $1,187.55   $1,187.60