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 $52.97   7.229%   $56.7992   $56.80   $56.80   $56.80  
  Purchase #2 $224.87   11.581%   $250.9122   $250.91   $250.90   $250.90  
  Purchase #3 $183.38   8.845%   $199.6   $199.60   $199.60   $199.60  
  Purchase #4 $16.98   4.795%   $17.7942   $17.79   $17.80   $17.80  
  Purchase #5 $190.62   4.297%   $198.8109   $198.81   $198.80   $198.80  
  Purchase #6 $210.27   9.671%   $230.6052   $230.61   $230.60   $230.60  
  Purchase #7 $101.74   6.605%   $108.4599   $108.46   $108.45   $108.50  
  7 purchase totals = $980.83       $1,062.9816   $1,062.98   $1,062.95   $1,063.00