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 $228.70   6.708%   $244.0412   $244.04   $244.05   $244.00  
  Purchase #2 $128.59   9.687%   $141.0465   $141.05   $141.05   $141.00  
  Purchase #3 $90.94   4.522%   $95.0523   $95.05   $95.05   $95.10  
  Purchase #4 $237.31   3.446%   $245.4877   $245.49   $245.50   $245.50  
  Purchase #5 $236.93   5.838%   $250.762   $250.76   $250.75   $250.80  
  Purchase #6 $157.25   5.640%   $166.1189   $166.12   $166.10   $166.10  
  Purchase #7 $190.60   3.519%   $197.3072   $197.31   $197.30   $197.30  
  7 purchase totals = $1,270.32       $1,339.8158   $1,339.82   $1,339.80   $1,339.80