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 $206.80   10.146%   $227.7819   $227.78   $227.80   $227.80  
  Purchase #2 $163.40   8.163%   $176.7383   $176.74   $176.75   $176.70  
  Purchase #3 $51.45   6.575%   $54.8328   $54.83   $54.85   $54.80  
  Purchase #4 $220.98   5.802%   $233.8013   $233.80   $233.80   $233.80  
  Purchase #5 $88.68   6.213%   $94.1897   $94.19   $94.20   $94.20  
  Purchase #6 $59.99   10.342%   $66.1942   $66.19   $66.20   $66.20  
  Purchase #7 $178.41   8.133%   $192.9201   $192.92   $192.90   $192.90  
  7 purchase totals = $969.71       $1,046.4583   $1,046.45   $1,046.50   $1,046.40