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 $114.92   3.815%   $119.3042   $119.30   $119.30   $119.30  
  Purchase #2 $169.63   6.747%   $181.0749   $181.07   $181.05   $181.10  
  Purchase #3 $193.39   5.749%   $204.508   $204.51   $204.50   $204.50  
  Purchase #4 $72.96   10.721%   $80.782   $80.78   $80.80   $80.80  
  Purchase #5 $136.26   8.241%   $147.4892   $147.49   $147.50   $147.50  
  Purchase #6 $16.43   9.102%   $17.9255   $17.93   $17.95   $17.90  
  Purchase #7 $67.75   12.735%   $76.378   $76.38   $76.40   $76.40  
  7 purchase totals = $771.34       $827.4618   $827.46   $827.50   $827.50