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 $114.69   3.285%   $118.4576   $118.46   $118.45   $118.50  
  Purchase #2 $21.97   7.245%   $23.5617   $23.56   $23.55   $23.60  
  Purchase #3 $224.72   11.291%   $250.0931   $250.09   $250.10   $250.10  
  Purchase #4 $65.67   13.632%   $74.6221   $74.62   $74.60   $74.60  
  Purchase #5 $180.48   11.428%   $201.1053   $201.11   $201.10   $201.10  
  Purchase #6 $68.69   3.381%   $71.0124   $71.01   $71.00   $71.00  
  Purchase #7 $241.71   13.213%   $273.6471   $273.65   $273.65   $273.60  
  7 purchase totals = $917.93       $1,012.4993   $1,012.50   $1,012.45   $1,012.50