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 $34.71   6.416%   $36.937   $36.94   $36.95   $36.90  
  Purchase #2 $204.76   9.376%   $223.9583   $223.96   $223.95   $224.00  
  Purchase #3 $105.37   8.538%   $114.3665   $114.37   $114.35   $114.40  
  Purchase #4 $188.83   4.702%   $197.7088   $197.71   $197.70   $197.70  
  Purchase #5 $248.40   13.283%   $281.395   $281.40   $281.40   $281.40  
  Purchase #6 $67.73   13.425%   $76.8228   $76.82   $76.80   $76.80  
  Purchase #7 $160.84   6.426%   $171.1756   $171.18   $171.20   $171.20  
  7 purchase totals = $1,010.64       $1,102.3640   $1,102.38   $1,102.35   $1,102.40