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 $164.25   4.230%   $171.1978   $171.20   $171.20   $171.20  
  Purchase #2 $210.87   10.735%   $233.5069   $233.51   $233.50   $233.50  
  Purchase #3 $139.64   8.396%   $151.3642   $151.36   $151.35   $151.40  
  Purchase #4 $84.91   3.153%   $87.5872   $87.59   $87.60   $87.60  
  Purchase #5 $234.54   8.340%   $254.1006   $254.10   $254.10   $254.10  
  Purchase #6 $214.60   10.415%   $236.9506   $236.95   $236.95   $237.00  
  Purchase #7 $206.45   7.612%   $222.165   $222.17   $222.15   $222.20  
  7 purchase totals = $1,255.26       $1,356.8723   $1,356.88   $1,356.85   $1,357.00