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 $126.46   10.410%   $139.6245   $139.62   $139.60   $139.60  
  Purchase #2 $155.93   4.279%   $162.6022   $162.60   $162.60   $162.60  
  Purchase #3 $235.77   13.117%   $266.696   $266.70   $266.70   $266.70  
  Purchase #4 $246.43   7.698%   $265.4002   $265.40   $265.40   $265.40  
  Purchase #5 $60.48   4.561%   $63.2385   $63.24   $63.25   $63.20  
  Purchase #6 $179.36   3.613%   $185.8403   $185.84   $185.85   $185.80  
  Purchase #7 $118.36   9.309%   $129.3781   $129.38   $129.40   $129.40  
  7 purchase totals = $1,122.79       $1,212.7798   $1,212.78   $1,212.80   $1,212.70