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 $170.92   11.508%   $190.5895   $190.59   $190.60   $190.60  
  Purchase #2 $241.64   8.324%   $261.7541   $261.75   $261.75   $261.80  
  Purchase #3 $249.42   9.612%   $273.3943   $273.39   $273.40   $273.40  
  Purchase #4 $35.59   12.173%   $39.9224   $39.92   $39.90   $39.90  
  Purchase #5 $129.95   8.129%   $140.5136   $140.51   $140.50   $140.50  
  Purchase #6 $92.68   11.405%   $103.2502   $103.25   $103.25   $103.30  
  Purchase #7 $183.99   5.529%   $194.1628   $194.16   $194.15   $194.20  
  7 purchase totals = $1,104.19       $1,203.5869   $1,203.57   $1,203.55   $1,203.70