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 $248.27   6.734%   $264.9885   $264.99   $265.00   $265.00  
  Purchase #2 $14.77   6.373%   $15.7113   $15.71   $15.70   $15.70  
  Purchase #3 $226.78   9.483%   $248.2855   $248.29   $248.30   $248.30  
  Purchase #4 $62.29   8.356%   $67.495   $67.50   $67.50   $67.50  
  Purchase #5 $182.64   12.805%   $206.0271   $206.03   $206.05   $206.00  
  Purchase #6 $244.79   4.709%   $256.3172   $256.32   $256.30   $256.30  
  Purchase #7 $104.93   11.255%   $116.7399   $116.74   $116.75   $116.70  
  7 purchase totals = $1,084.47       $1,175.5645   $1,175.58   $1,175.60   $1,175.50