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 $33.41   6.436%   $35.5603   $35.56   $35.55   $35.60  
  Purchase #2 $59.37   6.131%   $63.01   $63.01   $63.00   $63.00  
  Purchase #3 $242.47   3.360%   $250.617   $250.62   $250.60   $250.60  
  Purchase #4 $195.62   6.645%   $208.6189   $208.62   $208.60   $208.60  
  Purchase #5 $118.85   3.370%   $122.8552   $122.86   $122.85   $122.90  
  Purchase #6 $50.64   6.503%   $53.9331   $53.93   $53.95   $53.90  
  Purchase #7 $182.77   10.677%   $202.2844   $202.28   $202.30   $202.30  
  7 purchase totals = $883.13       $936.8789   $936.88   $936.85   $936.90