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 $164.73   10.311%   $181.7153   $181.72   $181.70   $181.70  
  Purchase #2 $221.36   8.389%   $239.9299   $239.93   $239.95   $239.90  
  Purchase #3 $169.91   8.581%   $184.49   $184.49   $184.50   $184.50  
  Purchase #4 $186.85   4.826%   $195.8674   $195.87   $195.85   $195.90  
  Purchase #5 $148.51   11.310%   $165.3065   $165.31   $165.30   $165.30  
  Purchase #6 $43.72   3.192%   $45.1155   $45.12   $45.10   $45.10  
  Purchase #7 $221.55   7.323%   $237.7741   $237.77   $237.75   $237.80  
  7 purchase totals = $1,156.63       $1,250.1987   $1,250.21   $1,250.15   $1,250.20