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 $244.69   6.507%   $260.612   $260.61   $260.60   $260.60  
  Purchase #2 $131.44   13.626%   $149.35   $149.35   $149.35   $149.40  
  Purchase #3 $94.54   9.232%   $103.2679   $103.27   $103.25   $103.30  
  Purchase #4 $233.47   12.228%   $262.0187   $262.02   $262.00   $262.00  
  Purchase #5 $25.40   9.133%   $27.7198   $27.72   $27.70   $27.70  
  Purchase #6 $158.50   11.630%   $176.9336   $176.93   $176.95   $176.90  
  Purchase #7 $14.91   9.742%   $16.3625   $16.36   $16.35   $16.40  
  7 purchase totals = $902.95       $996.2645   $996.26   $996.20   $996.30