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 $99.62   9.200%   $108.785   $108.79   $108.80   $108.80  
  Purchase #2 $47.85   4.436%   $49.9726   $49.97   $49.95   $50.00  
  Purchase #3 $84.65   3.229%   $87.3833   $87.38   $87.40   $87.40  
  Purchase #4 $18.53   8.702%   $20.1425   $20.14   $20.15   $20.10  
  Purchase #5 $28.71   12.626%   $32.3349   $32.33   $32.35   $32.30  
  Purchase #6 $181.85   10.130%   $200.2714   $200.27   $200.25   $200.30  
  Purchase #7 $35.60   11.597%   $39.7285   $39.73   $39.75   $39.70  
  7 purchase totals = $496.81       $538.6182   $538.61   $538.65   $538.60