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 $250.44   5.366%   $263.8786   $263.88   $263.90   $263.90  
  Purchase #2 $77.51   7.215%   $83.1023   $83.10   $83.10   $83.10  
  Purchase #3 $39.32   5.350%   $41.4236   $41.42   $41.40   $41.40  
  Purchase #4 $179.92   13.602%   $204.3927   $204.39   $204.40   $204.40  
  Purchase #5 $120.63   6.660%   $128.664   $128.66   $128.65   $128.70  
  Purchase #6 $242.42   3.687%   $251.358   $251.36   $251.35   $251.40  
  Purchase #7 $241.80   8.222%   $261.6808   $261.68   $261.70   $261.70  
  7 purchase totals = $1,152.04       $1,234.5000   $1,234.49   $1,234.50   $1,234.60