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 $81.44   6.237%   $86.5194   $86.52   $86.50   $86.50  
  Purchase #2 $162.53   12.550%   $182.9275   $182.93   $182.95   $182.90  
  Purchase #3 $59.26   5.874%   $62.7409   $62.74   $62.75   $62.70  
  Purchase #4 $225.29   4.268%   $234.9054   $234.91   $234.90   $234.90  
  Purchase #5 $243.56   7.429%   $261.6541   $261.65   $261.65   $261.70  
  Purchase #6 $146.44   4.283%   $152.712   $152.71   $152.70   $152.70  
  Purchase #7 $34.38   4.366%   $35.881   $35.88   $35.90   $35.90  
  7 purchase totals = $952.90       $1,017.3403   $1,017.34   $1,017.35   $1,017.30