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 $136.29   3.308%   $140.7985   $140.80   $140.80   $140.80  
  Purchase #2 $202.50   8.282%   $219.2711   $219.27   $219.25   $219.30  
  Purchase #3 $48.42   8.567%   $52.5681   $52.57   $52.55   $52.60  
  Purchase #4 $155.64   12.331%   $174.832   $174.83   $174.85   $174.80  
  Purchase #5 $225.88   4.526%   $236.1033   $236.10   $236.10   $236.10  
  Purchase #6 $195.88   13.235%   $221.8047   $221.80   $221.80   $221.80  
  Purchase #7 $23.53   4.277%   $24.5364   $24.54   $24.55   $24.50  
  7 purchase totals = $988.14       $1,069.9141   $1,069.91   $1,069.90   $1,069.90