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 $22.55   6.466%   $24.0081   $24.01   $24.00   $24.00  
  Purchase #2 $141.52   12.116%   $158.6666   $158.67   $158.65   $158.70  
  Purchase #3 $124.33   9.215%   $135.787   $135.79   $135.80   $135.80  
  Purchase #4 $9.68   6.323%   $10.2921   $10.29   $10.30   $10.30  
  Purchase #5 $186.31   11.746%   $208.194   $208.19   $208.20   $208.20  
  Purchase #6 $111.73   10.306%   $123.2449   $123.24   $123.25   $123.20  
  Purchase #7 $58.50   6.550%   $62.3318   $62.33   $62.35   $62.30  
  7 purchase totals = $654.62       $722.5245   $722.52   $722.55   $722.50