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 $54.63   7.711%   $58.8425   $58.84   $58.85   $58.80  
  Purchase #2 $172.88   12.327%   $194.1909   $194.19   $194.20   $194.20  
  Purchase #3 $229.69   10.866%   $254.6481   $254.65   $254.65   $254.60  
  Purchase #4 $61.57   11.221%   $68.4788   $68.48   $68.50   $68.50  
  Purchase #5 $81.34   12.185%   $91.2513   $91.25   $91.25   $91.30  
  Purchase #6 $141.59   5.329%   $149.1353   $149.14   $149.15   $149.10  
  Purchase #7 $198.67   9.378%   $217.3013   $217.30   $217.30   $217.30  
  7 purchase totals = $940.37       $1,033.8482   $1,033.85   $1,033.90   $1,033.80