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 $63.59   12.837%   $71.753   $71.75   $71.75   $71.80  
  Purchase #2 $11.43   6.321%   $12.1525   $12.15   $12.15   $12.20  
  Purchase #3 $103.63   11.581%   $115.6314   $115.63   $115.65   $115.60  
  Purchase #4 $47.87   12.325%   $53.77   $53.77   $53.75   $53.80  
  Purchase #5 $127.82   11.719%   $142.7992   $142.80   $142.80   $142.80  
  Purchase #6 $32.99   4.828%   $34.5828   $34.58   $34.60   $34.60  
  Purchase #7 $22.30   6.792%   $23.8146   $23.81   $23.80   $23.80  
  7 purchase totals = $409.63       $454.5035   $454.49   $454.50   $454.60