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 $65.65   4.826%   $68.8183   $68.82   $68.80   $68.80  
  Purchase #2 $212.74   6.856%   $227.3255   $227.33   $227.35   $227.30  
  Purchase #3 $96.54   5.824%   $102.1625   $102.16   $102.15   $102.20  
  Purchase #4 $111.72   11.296%   $124.3399   $124.34   $124.35   $124.30  
  Purchase #5 $210.79   8.703%   $229.1351   $229.14   $229.15   $229.10  
  Purchase #6 $191.87   7.641%   $206.5308   $206.53   $206.55   $206.50  
  Purchase #7 $69.47   10.450%   $76.7296   $76.73   $76.75   $76.70  
  7 purchase totals = $958.78       $1,035.0417   $1,035.05   $1,035.10   $1,034.90