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 $67.37   10.102%   $74.1757   $74.18   $74.20   $74.20  
  Purchase #2 $198.93   8.521%   $215.8808   $215.88   $215.90   $215.90  
  Purchase #3 $114.79   5.726%   $121.3629   $121.36   $121.35   $121.40  
  Purchase #4 $187.59   10.299%   $206.9099   $206.91   $206.90   $206.90  
  Purchase #5 $141.81   5.343%   $149.3869   $149.39   $149.40   $149.40  
  Purchase #6 $173.72   11.321%   $193.3868   $193.39   $193.40   $193.40  
  Purchase #7 $250.27   11.641%   $279.4039   $279.40   $279.40   $279.40  
  7 purchase totals = $1,134.48       $1,240.5069   $1,240.51   $1,240.55   $1,240.60