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 $213.58   12.860%   $241.0464   $241.05   $241.05   $241.00  
  Purchase #2 $186.89   9.397%   $204.4521   $204.45   $204.45   $204.50  
  Purchase #3 $236.78   9.730%   $259.8187   $259.82   $259.80   $259.80  
  Purchase #4 $163.73   4.680%   $171.3926   $171.39   $171.40   $171.40  
  Purchase #5 $179.86   7.274%   $192.943   $192.94   $192.95   $192.90  
  Purchase #6 $89.44   13.442%   $101.4625   $101.46   $101.45   $101.50  
  Purchase #7 $13.46   11.213%   $14.9693   $14.97   $14.95   $15.00  
  7 purchase totals = $1,083.74       $1,186.0846   $1,186.08   $1,186.05   $1,186.10