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 $104.52   3.758%   $108.4479   $108.45   $108.45   $108.40  
  Purchase #2 $192.56   12.453%   $216.5395   $216.54   $216.55   $216.50  
  Purchase #3 $207.81   3.465%   $215.0106   $215.01   $215.00   $215.00  
  Purchase #4 $194.41   7.250%   $208.5047   $208.50   $208.50   $208.50  
  Purchase #5 $154.55   4.464%   $161.4491   $161.45   $161.45   $161.40  
  Purchase #6 $39.67   13.291%   $44.9425   $44.94   $44.95   $44.90  
  Purchase #7 $13.45   11.440%   $14.9887   $14.99   $15.00   $15.00  
  7 purchase totals = $906.97       $969.8830   $969.88   $969.90   $969.70