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 $207.95   8.223%   $225.0497   $225.05   $225.05   $225.00  
  Purchase #2 $123.57   5.632%   $130.5295   $130.53   $130.55   $130.50  
  Purchase #3 $198.85   6.428%   $211.6321   $211.63   $211.65   $211.60  
  Purchase #4 $201.91   5.301%   $212.6132   $212.61   $212.60   $212.60  
  Purchase #5 $167.55   4.259%   $174.686   $174.69   $174.70   $174.70  
  Purchase #6 $151.89   5.121%   $159.6683   $159.67   $159.65   $159.70  
  Purchase #7 $66.29   5.165%   $69.7139   $69.71   $69.70   $69.70  
  7 purchase totals = $1,118.01       $1,183.8927   $1,183.89   $1,183.90   $1,183.80