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 $68.74   9.164%   $75.0393   $75.04   $75.05   $75.00  
  Purchase #2 $149.78   13.257%   $169.6363   $169.64   $169.65   $169.60  
  Purchase #3 $219.67   13.304%   $248.8949   $248.89   $248.90   $248.90  
  Purchase #4 $81.35   3.157%   $83.9182   $83.92   $83.90   $83.90  
  Purchase #5 $51.95   12.811%   $58.6053   $58.61   $58.60   $58.60  
  Purchase #6 $214.40   6.754%   $228.8806   $228.88   $228.90   $228.90  
  Purchase #7 $68.63   11.120%   $76.2617   $76.26   $76.25   $76.30  
  7 purchase totals = $854.52       $941.2363   $941.24   $941.25   $941.20