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 $207.82   12.872%   $234.5706   $234.57   $234.55   $234.60  
  Purchase #2 $237.73   9.773%   $260.9634   $260.96   $260.95   $261.00  
  Purchase #3 $92.47   6.413%   $98.4001   $98.40   $98.40   $98.40  
  Purchase #4 $236.33   7.696%   $254.518   $254.52   $254.50   $254.50  
  Purchase #5 $181.50   7.383%   $194.9001   $194.90   $194.90   $194.90  
  Purchase #6 $101.29   3.848%   $105.1876   $105.19   $105.20   $105.20  
  Purchase #7 $19.87   8.719%   $21.6025   $21.60   $21.60   $21.60  
  7 purchase totals = $1,077.01       $1,170.1423   $1,170.14   $1,170.10   $1,170.20