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 $59.27   6.620%   $63.1937   $63.19   $63.20   $63.20  
  Purchase #2 $131.99   7.252%   $141.5619   $141.56   $141.55   $141.60  
  Purchase #3 $161.51   6.267%   $171.6318   $171.63   $171.65   $171.60  
  Purchase #4 $187.40   11.143%   $208.282   $208.28   $208.30   $208.30  
  Purchase #5 $116.55   6.250%   $123.8344   $123.83   $123.85   $123.80  
  Purchase #6 $116.87   3.636%   $121.1194   $121.12   $121.10   $121.10  
  Purchase #7 $158.87   6.337%   $168.9376   $168.94   $168.95   $168.90  
  7 purchase totals = $932.46       $998.5608   $998.55   $998.60   $998.50