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 $32.74   13.591%   $37.1897   $37.19   $37.20   $37.20  
  Purchase #2 $71.86   6.532%   $76.5539   $76.55   $76.55   $76.60  
  Purchase #3 $113.95   4.497%   $119.0743   $119.07   $119.05   $119.10  
  Purchase #4 $201.41   4.794%   $211.0656   $211.07   $211.05   $211.10  
  Purchase #5 $219.41   7.774%   $236.4669   $236.47   $236.45   $236.50  
  Purchase #6 $5.30   3.608%   $5.4912   $5.49   $5.50   $5.50  
  Purchase #7 $166.73   8.269%   $180.5169   $180.52   $180.50   $180.50  
  7 purchase totals = $811.40       $866.3585   $866.36   $866.30   $866.50