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 $208.79   9.178%   $227.9527   $227.95   $227.95   $228.00  
  Purchase #2 $230.79   8.442%   $250.2733   $250.27   $250.25   $250.30  
  Purchase #3 $10.63   9.114%   $11.5988   $11.60   $11.60   $11.60  
  Purchase #4 $35.82   5.282%   $37.712   $37.71   $37.70   $37.70  
  Purchase #5 $205.64   6.732%   $219.4837   $219.48   $219.50   $219.50  
  Purchase #6 $43.86   10.316%   $48.3846   $48.38   $48.40   $48.40  
  Purchase #7 $236.42   4.590%   $247.2717   $247.27   $247.25   $247.30  
  7 purchase totals = $971.95       $1,042.6768   $1,042.66   $1,042.65   $1,042.80