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 $106.65   9.213%   $116.4757   $116.48   $116.50   $116.50  
  Purchase #2 $11.78   6.353%   $12.5284   $12.53   $12.55   $12.50  
  Purchase #3 $86.67   7.302%   $92.9986   $93.00   $93.00   $93.00  
  Purchase #4 $163.41   13.673%   $185.753   $185.75   $185.75   $185.80  
  Purchase #5 $101.30   4.410%   $105.7673   $105.77   $105.75   $105.80  
  Purchase #6 $204.39   5.488%   $215.6069   $215.61   $215.60   $215.60  
  Purchase #7 $130.25   6.582%   $138.8231   $138.82   $138.80   $138.80  
  7 purchase totals = $804.45       $867.9530   $867.96   $867.95   $868.00