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 $84.79   10.537%   $93.7243   $93.72   $93.70   $93.70  
  Purchase #2 $60.63   9.209%   $66.2134   $66.21   $66.20   $66.20  
  Purchase #3 $52.59   8.548%   $57.0854   $57.09   $57.10   $57.10  
  Purchase #4 $49.65   6.426%   $52.8405   $52.84   $52.85   $52.80  
  Purchase #5 $166.68   10.402%   $184.0181   $184.02   $184.00   $184.00  
  Purchase #6 $174.40   10.579%   $192.8498   $192.85   $192.85   $192.80  
  Purchase #7 $87.34   3.691%   $90.5637   $90.56   $90.55   $90.60  
  7 purchase totals = $676.08       $737.2952   $737.29   $737.25   $737.20