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 $82.41   13.616%   $93.6309   $93.63   $93.65   $93.60  
  Purchase #2 $193.49   6.463%   $205.9953   $206.00   $206.00   $206.00  
  Purchase #3 $127.32   3.662%   $131.9825   $131.98   $132.00   $132.00  
  Purchase #4 $152.76   11.427%   $170.2159   $170.22   $170.20   $170.20  
  Purchase #5 $60.64   7.348%   $65.0958   $65.10   $65.10   $65.10  
  Purchase #6 $225.50   4.856%   $236.4503   $236.45   $236.45   $236.50  
  Purchase #7 $89.82   7.282%   $96.3607   $96.36   $96.35   $96.40  
  7 purchase totals = $931.94       $999.7314   $999.74   $999.75   $999.80