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 $223.65   11.205%   $248.71   $248.71   $248.70   $248.70  
  Purchase #2 $53.91   5.633%   $56.9468   $56.95   $56.95   $56.90  
  Purchase #3 $167.61   7.222%   $179.7148   $179.71   $179.70   $179.70  
  Purchase #4 $234.41   13.863%   $266.9063   $266.91   $266.90   $266.90  
  Purchase #5 $198.64   9.473%   $217.4572   $217.46   $217.45   $217.50  
  Purchase #6 $222.82   10.403%   $246   $246.00   $246.00   $246.00  
  Purchase #7 $102.86   7.687%   $110.7668   $110.77   $110.75   $110.80  
  7 purchase totals = $1,203.90       $1,326.5019   $1,326.51   $1,326.45   $1,326.50