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 $186.63   13.426%   $211.6869   $211.69   $211.70   $211.70  
  Purchase #2 $52.98   10.770%   $58.6859   $58.69   $58.70   $58.70  
  Purchase #3 $176.46   13.178%   $199.7139   $199.71   $199.70   $199.70  
  Purchase #4 $217.85   13.855%   $248.0331   $248.03   $248.05   $248.00  
  Purchase #5 $238.98   10.434%   $263.9152   $263.92   $263.90   $263.90  
  Purchase #6 $122.42   9.431%   $133.9654   $133.97   $133.95   $134.00  
  Purchase #7 $159.57   11.558%   $178.0131   $178.01   $178.00   $178.00  
  7 purchase totals = $1,154.89       $1,294.0135   $1,294.02   $1,294.00   $1,294.00