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 $185.45   9.807%   $203.6371   $203.64   $203.65   $203.60  
  Purchase #2 $117.62   5.725%   $124.3537   $124.35   $124.35   $124.40  
  Purchase #3 $97.39   10.665%   $107.7766   $107.78   $107.80   $107.80  
  Purchase #4 $91.82   12.562%   $103.3544   $103.35   $103.35   $103.40  
  Purchase #5 $246.49   6.454%   $262.3985   $262.40   $262.40   $262.40  
  Purchase #6 $249.91   10.526%   $276.2155   $276.22   $276.20   $276.20  
  Purchase #7 $192.46   7.137%   $206.1959   $206.20   $206.20   $206.20  
  7 purchase totals = $1,181.14       $1,283.9317   $1,283.94   $1,283.95   $1,284.00