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 $226.82   11.805%   $253.5961   $253.60   $253.60   $253.60  
  Purchase #2 $206.73   10.290%   $228.0025   $228.00   $228.00   $228.00  
  Purchase #3 $48.48   5.668%   $51.2278   $51.23   $51.25   $51.20  
  Purchase #4 $236.79   8.619%   $257.1989   $257.20   $257.20   $257.20  
  Purchase #5 $133.38   9.110%   $145.5309   $145.53   $145.55   $145.50  
  Purchase #6 $130.28   5.632%   $137.6174   $137.62   $137.60   $137.60  
  Purchase #7 $169.32   12.506%   $190.4952   $190.50   $190.50   $190.50  
  7 purchase totals = $1,151.80       $1,263.6688   $1,263.68   $1,263.70   $1,263.60