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 $89.30   7.283%   $95.8037   $95.80   $95.80   $95.80  
  Purchase #2 $141.38   8.822%   $153.8525   $153.85   $153.85   $153.90  
  Purchase #3 $212.64   13.138%   $240.5766   $240.58   $240.60   $240.60  
  Purchase #4 $15.49   5.477%   $16.3384   $16.34   $16.35   $16.30  
  Purchase #5 $205.51   9.427%   $224.8834   $224.88   $224.90   $224.90  
  Purchase #6 $41.92   12.577%   $47.1923   $47.19   $47.20   $47.20  
  Purchase #7 $44.80   9.702%   $49.1465   $49.15   $49.15   $49.10  
  7 purchase totals = $751.04       $827.7934   $827.79   $827.85   $827.80