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 $128.61   5.747%   $136.0012   $136.00   $136.00   $136.00  
  Purchase #2 $50.42   12.358%   $56.6509   $56.65   $56.65   $56.70  
  Purchase #3 $14.56   3.459%   $15.0636   $15.06   $15.05   $15.10  
  Purchase #4 $197.48   8.530%   $214.325   $214.33   $214.35   $214.30  
  Purchase #5 $243.73   10.261%   $268.7391   $268.74   $268.75   $268.70  
  Purchase #6 $157.90   6.522%   $168.1982   $168.20   $168.20   $168.20  
  Purchase #7 $114.26   6.627%   $121.832   $121.83   $121.85   $121.80  
  7 purchase totals = $906.96       $980.8100   $980.81   $980.85   $980.80