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 $17.62   5.767%   $18.6361   $18.64   $18.65   $18.60  
  Purchase #2 $93.62   8.419%   $101.5019   $101.50   $101.50   $101.50  
  Purchase #3 $212.94   5.518%   $224.69   $224.69   $224.70   $224.70  
  Purchase #4 $225.74   5.533%   $238.2302   $238.23   $238.25   $238.20  
  Purchase #5 $47.88   11.333%   $53.3062   $53.31   $53.30   $53.30  
  Purchase #6 $191.42   5.804%   $202.53   $202.53   $202.55   $202.50  
  Purchase #7 $137.84   4.329%   $143.8071   $143.81   $143.80   $143.80  
  7 purchase totals = $927.06       $982.7015   $982.71   $982.75   $982.60