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 $186.54   10.504%   $206.1342   $206.13   $206.15   $206.10  
  Purchase #2 $76.94   6.152%   $81.6733   $81.67   $81.65   $81.70  
  Purchase #3 $36.59   11.487%   $40.7931   $40.79   $40.80   $40.80  
  Purchase #4 $109.68   3.752%   $113.7952   $113.80   $113.80   $113.80  
  Purchase #5 $5.69   9.141%   $6.2101   $6.21   $6.20   $6.20  
  Purchase #6 $137.47   9.428%   $150.4307   $150.43   $150.45   $150.40  
  Purchase #7 $144.92   5.561%   $152.979   $152.98   $153.00   $153.00  
  7 purchase totals = $697.83       $752.0156   $752.01   $752.05   $752.00