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 $119.96   5.527%   $126.5902   $126.59   $126.60   $126.60  
  Purchase #2 $215.39   8.646%   $234.0126   $234.01   $234.00   $234.00  
  Purchase #3 $104.78   10.305%   $115.5776   $115.58   $115.60   $115.60  
  Purchase #4 $84.34   9.598%   $92.435   $92.44   $92.45   $92.40  
  Purchase #5 $185.70   10.145%   $204.5393   $204.54   $204.55   $204.50  
  Purchase #6 $78.71   4.336%   $82.1229   $82.12   $82.10   $82.10  
  Purchase #7 $78.45   11.417%   $87.4066   $87.41   $87.40   $87.40  
  7 purchase totals = $867.33       $942.6842   $942.69   $942.70   $942.60