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 $24.67   4.584%   $25.8009   $25.80   $25.80   $25.80  
  Purchase #2 $118.94   4.856%   $124.7157   $124.72   $124.70   $124.70  
  Purchase #3 $158.26   6.644%   $168.7748   $168.77   $168.75   $168.80  
  Purchase #4 $74.64   6.340%   $79.3722   $79.37   $79.35   $79.40  
  Purchase #5 $168.50   4.146%   $175.486   $175.49   $175.50   $175.50  
  Purchase #6 $65.74   12.103%   $73.6965   $73.70   $73.70   $73.70  
  Purchase #7 $44.45   9.395%   $48.6261   $48.63   $48.65   $48.60  
  7 purchase totals = $655.20       $696.4722   $696.48   $696.45   $696.50