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 $199.25   13.398%   $225.9455   $225.95   $225.95   $225.90  
  Purchase #2 $188.99   8.306%   $204.6875   $204.69   $204.70   $204.70  
  Purchase #3 $67.45   4.135%   $70.2391   $70.24   $70.25   $70.20  
  Purchase #4 $51.76   12.238%   $58.0944   $58.09   $58.10   $58.10  
  Purchase #5 $161.50   10.645%   $178.6917   $178.69   $178.70   $178.70  
  Purchase #6 $128.43   3.603%   $133.0573   $133.06   $133.05   $133.10  
  Purchase #7 $126.36   6.103%   $134.0718   $134.07   $134.05   $134.10  
  7 purchase totals = $923.74       $1,004.7873   $1,004.79   $1,004.80   $1,004.80