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 $81.47   12.686%   $91.8053   $91.81   $91.80   $91.80  
  Purchase #2 $170.91   11.707%   $190.9184   $190.92   $190.90   $190.90  
  Purchase #3 $106.73   7.185%   $114.3986   $114.40   $114.40   $114.40  
  Purchase #4 $205.42   5.125%   $215.9478   $215.95   $215.95   $215.90  
  Purchase #5 $212.42   6.595%   $226.4291   $226.43   $226.45   $226.40  
  Purchase #6 $130.40   11.298%   $145.1326   $145.13   $145.15   $145.10  
  Purchase #7 $24.46   4.725%   $25.6157   $25.62   $25.60   $25.60  
  7 purchase totals = $931.81       $1,010.2475   $1,010.26   $1,010.25   $1,010.10