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 $220.85   11.159%   $245.4947   $245.49   $245.50   $245.50  
  Purchase #2 $231.79   5.622%   $244.8212   $244.82   $244.80   $244.80  
  Purchase #3 $116.26   10.403%   $128.3545   $128.35   $128.35   $128.40  
  Purchase #4 $237.67   4.550%   $248.484   $248.48   $248.50   $248.50  
  Purchase #5 $95.68   9.201%   $104.4835   $104.48   $104.50   $104.50  
  Purchase #6 $95.70   8.490%   $103.8249   $103.82   $103.80   $103.80  
  Purchase #7 $127.29   5.201%   $133.9104   $133.91   $133.90   $133.90  
  7 purchase totals = $1,125.24       $1,209.3732   $1,209.35   $1,209.35   $1,209.40