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 $20.79   5.439%   $21.9208   $21.92   $21.90   $21.90  
  Purchase #2 $12.97   6.208%   $13.7752   $13.78   $13.80   $13.80  
  Purchase #3 $30.66   13.537%   $34.8104   $34.81   $34.80   $34.80  
  Purchase #4 $20.91   7.819%   $22.545   $22.55   $22.55   $22.50  
  Purchase #5 $155.86   5.451%   $164.3559   $164.36   $164.35   $164.40  
  Purchase #6 $186.44   11.449%   $207.7855   $207.79   $207.80   $207.80  
  Purchase #7 $245.87   10.494%   $271.6716   $271.67   $271.65   $271.70  
  7 purchase totals = $673.50       $736.8644   $736.88   $736.85   $736.90