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 $249.61   5.360%   $262.9891   $262.99   $263.00   $263.00  
  Purchase #2 $204.49   4.584%   $213.8638   $213.86   $213.85   $213.90  
  Purchase #3 $50.44   4.329%   $52.6235   $52.62   $52.60   $52.60  
  Purchase #4 $231.83   5.228%   $243.9501   $243.95   $243.95   $244.00  
  Purchase #5 $68.38   9.277%   $74.7236   $74.72   $74.70   $74.70  
  Purchase #6 $16.59   3.281%   $17.1343   $17.13   $17.15   $17.10  
  Purchase #7 $24.39   13.515%   $27.6863   $27.69   $27.70   $27.70  
  7 purchase totals = $845.73       $892.9707   $892.96   $892.95   $893.00