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 $248.40   13.817%   $282.7214   $282.72   $282.70   $282.70  
  Purchase #2 $235.61   9.283%   $257.4817   $257.48   $257.50   $257.50  
  Purchase #3 $67.51   11.664%   $75.3844   $75.38   $75.40   $75.40  
  Purchase #4 $249.68   13.273%   $282.82   $282.82   $282.80   $282.80  
  Purchase #5 $54.55   6.336%   $58.0063   $58.01   $58.00   $58.00  
  Purchase #6 $141.86   5.189%   $149.2211   $149.22   $149.20   $149.20  
  Purchase #7 $248.99   5.114%   $261.7233   $261.72   $261.70   $261.70  
  7 purchase totals = $1,246.60       $1,367.3582   $1,367.35   $1,367.30   $1,367.30