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 $211.27   6.495%   $224.992   $224.99   $225.00   $225.00  
  Purchase #2 $62.34   7.368%   $66.9332   $66.93   $66.95   $66.90  
  Purchase #3 $86.44   10.256%   $95.3053   $95.31   $95.30   $95.30  
  Purchase #4 $235.86   13.460%   $267.6068   $267.61   $267.60   $267.60  
  Purchase #5 $26.85   4.446%   $28.0438   $28.04   $28.05   $28.00  
  Purchase #6 $16.31   13.656%   $18.5373   $18.54   $18.55   $18.50  
  Purchase #7 $65.63   8.593%   $71.2696   $71.27   $71.25   $71.30  
  7 purchase totals = $704.70       $772.6880   $772.69   $772.70   $772.60