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 $44.25   8.622%   $48.0652   $48.07   $48.05   $48.10  
  Purchase #2 $236.91   8.293%   $256.5569   $256.56   $256.55   $256.60  
  Purchase #3 $65.86   3.679%   $68.283   $68.28   $68.30   $68.30  
  Purchase #4 $115.57   9.858%   $126.9629   $126.96   $126.95   $127.00  
  Purchase #5 $120.99   12.173%   $135.7181   $135.72   $135.70   $135.70  
  Purchase #6 $71.66   5.811%   $75.8242   $75.82   $75.80   $75.80  
  Purchase #7 $115.55   3.209%   $119.258   $119.26   $119.25   $119.30  
  7 purchase totals = $770.79       $830.6683   $830.67   $830.60   $830.80