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 $44.40   8.755%   $48.2872   $48.29   $48.30   $48.30  
  Purchase #2 $212.41   11.834%   $237.5466   $237.55   $237.55   $237.50  
  Purchase #3 $65.83   5.135%   $69.2104   $69.21   $69.20   $69.20  
  Purchase #4 $84.75   7.821%   $91.3783   $91.38   $91.40   $91.40  
  Purchase #5 $233.95   10.409%   $258.3019   $258.30   $258.30   $258.30  
  Purchase #6 $186.75   4.709%   $195.5441   $195.54   $195.55   $195.50  
  Purchase #7 $23.80   4.113%   $24.7789   $24.78   $24.80   $24.80  
  7 purchase totals = $851.89       $925.0474   $925.05   $925.10   $925.00