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 $241.82   11.532%   $269.7067   $269.71   $269.70   $269.70  
  Purchase #2 $33.78   7.136%   $36.1905   $36.19   $36.20   $36.20  
  Purchase #3 $123.82   5.528%   $130.6648   $130.66   $130.65   $130.70  
  Purchase #4 $151.79   3.619%   $157.2833   $157.28   $157.30   $157.30  
  Purchase #5 $42.98   3.621%   $44.5363   $44.54   $44.55   $44.50  
  Purchase #6 $56.92   4.544%   $59.5064   $59.51   $59.50   $59.50  
  Purchase #7 $36.60   8.804%   $39.8223   $39.82   $39.80   $39.80  
  7 purchase totals = $687.71       $737.7103   $737.71   $737.70   $737.70