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 $178.55   9.683%   $195.839   $195.84   $195.85   $195.80  
  Purchase #2 $155.56   4.316%   $162.274   $162.27   $162.25   $162.30  
  Purchase #3 $180.42   11.803%   $201.715   $201.72   $201.70   $201.70  
  Purchase #4 $132.71   10.137%   $146.1628   $146.16   $146.15   $146.20  
  Purchase #5 $70.68   12.498%   $79.5136   $79.51   $79.50   $79.50  
  Purchase #6 $187.50   6.342%   $199.3913   $199.39   $199.40   $199.40  
  Purchase #7 $41.42   6.239%   $44.0042   $44.00   $44.00   $44.00  
  7 purchase totals = $946.84       $1,028.8999   $1,028.89   $1,028.85   $1,028.90