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 $62.44   3.236%   $64.4606   $64.46   $64.45   $64.50  
  Purchase #2 $121.55   4.416%   $126.9176   $126.92   $126.90   $126.90  
  Purchase #3 $34.67   7.563%   $37.2921   $37.29   $37.30   $37.30  
  Purchase #4 $104.90   7.512%   $112.7801   $112.78   $112.80   $112.80  
  Purchase #5 $168.58   8.462%   $182.8452   $182.85   $182.85   $182.80  
  Purchase #6 $34.68   10.150%   $38.2   $38.20   $38.20   $38.20  
  Purchase #7 $214.76   12.260%   $241.0896   $241.09   $241.10   $241.10  
  7 purchase totals = $741.58       $803.5852   $803.59   $803.60   $803.60