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 $233.69   13.729%   $265.7733   $265.77   $265.75   $265.80  
  Purchase #2 $219.57   5.183%   $230.9503   $230.95   $230.95   $231.00  
  Purchase #3 $149.76   6.714%   $159.8149   $159.81   $159.80   $159.80  
  Purchase #4 $67.99   10.825%   $75.3499   $75.35   $75.35   $75.30  
  Purchase #5 $102.95   11.130%   $114.4083   $114.41   $114.40   $114.40  
  Purchase #6 $231.94   9.809%   $254.691   $254.69   $254.70   $254.70  
  Purchase #7 $10.57   13.387%   $11.985   $11.99   $12.00   $12.00  
  7 purchase totals = $1,016.47       $1,112.9727   $1,112.97   $1,112.95   $1,113.00