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 $173.73   7.499%   $186.758   $186.76   $186.75   $186.80  
  Purchase #2 $114.56   12.159%   $128.4894   $128.49   $128.50   $128.50  
  Purchase #3 $159.56   5.267%   $167.964   $167.96   $167.95   $168.00  
  Purchase #4 $142.42   13.182%   $161.1938   $161.19   $161.20   $161.20  
  Purchase #5 $61.62   4.407%   $64.3356   $64.34   $64.35   $64.30  
  Purchase #6 $116.40   4.452%   $121.5821   $121.58   $121.60   $121.60  
  Purchase #7 $153.64   12.856%   $173.392   $173.39   $173.40   $173.40  
  7 purchase totals = $921.93       $1,003.7149   $1,003.71   $1,003.75   $1,003.80