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 $232.41   6.493%   $247.5004   $247.50   $247.50   $247.50  
  Purchase #2 $83.38   12.357%   $93.6833   $93.68   $93.70   $93.70  
  Purchase #3 $152.33   10.786%   $168.7603   $168.76   $168.75   $168.80  
  Purchase #4 $44.54   6.127%   $47.269   $47.27   $47.25   $47.30  
  Purchase #5 $73.88   3.718%   $76.6269   $76.63   $76.65   $76.60  
  Purchase #6 $75.87   3.581%   $78.5869   $78.59   $78.60   $78.60  
  Purchase #7 $211.69   8.144%   $228.93   $228.93   $228.95   $228.90  
  7 purchase totals = $874.10       $941.3568   $941.36   $941.40   $941.40