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 $178.37   9.189%   $194.7604   $194.76   $194.75   $194.80  
  Purchase #2 $160.35   5.611%   $169.3472   $169.35   $169.35   $169.30  
  Purchase #3 $29.26   10.508%   $32.3346   $32.33   $32.35   $32.30  
  Purchase #4 $92.95   5.486%   $98.0492   $98.05   $98.05   $98.00  
  Purchase #5 $192.25   5.325%   $202.4873   $202.49   $202.50   $202.50  
  Purchase #6 $19.30   8.463%   $20.9334   $20.93   $20.95   $20.90  
  Purchase #7 $165.29   11.672%   $184.5826   $184.58   $184.60   $184.60  
  7 purchase totals = $837.77       $902.4947   $902.49   $902.55   $902.40