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 $106.56   6.760%   $113.7635   $113.76   $113.75   $113.80  
  Purchase #2 $63.47   3.114%   $65.4465   $65.45   $65.45   $65.40  
  Purchase #3 $164.47   7.204%   $176.3184   $176.32   $176.30   $176.30  
  Purchase #4 $212.96   3.669%   $220.7735   $220.77   $220.75   $220.80  
  Purchase #5 $59.28   12.269%   $66.5531   $66.55   $66.55   $66.60  
  Purchase #6 $214.68   10.496%   $237.2128   $237.21   $237.20   $237.20  
  Purchase #7 $218.29   9.272%   $238.5298   $238.53   $238.55   $238.50  
  7 purchase totals = $1,039.71       $1,118.5976   $1,118.59   $1,118.55   $1,118.60