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 $229.73   4.474%   $240.0081   $240.01   $240.00   $240.00  
  Purchase #2 $56.49   6.844%   $60.3562   $60.36   $60.35   $60.40  
  Purchase #3 $214.32   7.349%   $230.0704   $230.07   $230.05   $230.10  
  Purchase #4 $33.55   11.246%   $37.323   $37.32   $37.30   $37.30  
  Purchase #5 $231.38   11.450%   $257.873   $257.87   $257.85   $257.90  
  Purchase #6 $126.41   9.384%   $138.2723   $138.27   $138.25   $138.30  
  Purchase #7 $48.71   4.564%   $50.9331   $50.93   $50.95   $50.90  
  7 purchase totals = $940.59       $1,014.8361   $1,014.83   $1,014.75   $1,014.90