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 $12.98   11.858%   $14.5192   $14.52   $14.50   $14.50  
  Purchase #2 $208.87   5.612%   $220.5918   $220.59   $220.60   $220.60  
  Purchase #3 $159.34   5.461%   $168.0416   $168.04   $168.05   $168.00  
  Purchase #4 $99.62   8.190%   $107.7789   $107.78   $107.80   $107.80  
  Purchase #5 $132.44   8.131%   $143.2087   $143.21   $143.20   $143.20  
  Purchase #6 $154.89   10.858%   $171.708   $171.71   $171.70   $171.70  
  Purchase #7 $119.70   12.299%   $134.4219   $134.42   $134.40   $134.40  
  7 purchase totals = $887.84       $960.2701   $960.27   $960.25   $960.20