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 $86.64   11.103%   $96.2596   $96.26   $96.25   $96.30  
  Purchase #2 $103.87   3.294%   $107.2915   $107.29   $107.30   $107.30  
  Purchase #3 $203.32   10.572%   $224.815   $224.82   $224.80   $224.80  
  Purchase #4 $61.80   6.257%   $65.6668   $65.67   $65.65   $65.70  
  Purchase #5 $248.86   3.158%   $256.719   $256.72   $256.70   $256.70  
  Purchase #6 $17.71   4.732%   $18.548   $18.55   $18.55   $18.50  
  Purchase #7 $130.53   7.518%   $140.3432   $140.34   $140.35   $140.30  
  7 purchase totals = $852.73       $909.6431   $909.65   $909.60   $909.60