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 $250.51   5.593%   $264.521   $264.52   $264.50   $264.50  
  Purchase #2 $87.89   11.439%   $97.9437   $97.94   $97.95   $97.90  
  Purchase #3 $80.83   10.781%   $89.5443   $89.54   $89.55   $89.50  
  Purchase #4 $208.46   8.565%   $226.3146   $226.31   $226.30   $226.30  
  Purchase #5 $63.30   7.872%   $68.283   $68.28   $68.30   $68.30  
  Purchase #6 $228.29   12.267%   $256.2943   $256.29   $256.30   $256.30  
  Purchase #7 $40.99   7.412%   $44.0282   $44.03   $44.05   $44.00  
  7 purchase totals = $960.27       $1,046.9291   $1,046.91   $1,046.95   $1,046.80