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 $237.61   7.490%   $255.407   $255.41   $255.40   $255.40  
  Purchase #2 $201.97   13.298%   $228.828   $228.83   $228.85   $228.80  
  Purchase #3 $34.49   6.591%   $36.7632   $36.76   $36.75   $36.80  
  Purchase #4 $51.31   13.658%   $58.3179   $58.32   $58.30   $58.30  
  Purchase #5 $238.94   10.713%   $264.5376   $264.54   $264.55   $264.50  
  Purchase #6 $22.68   9.803%   $24.9033   $24.90   $24.90   $24.90  
  Purchase #7 $14.65   5.860%   $15.5085   $15.51   $15.50   $15.50  
  7 purchase totals = $801.65       $884.2655   $884.27   $884.25   $884.20