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 $47.77   4.693%   $50.0118   $50.01   $50.00   $50.00  
  Purchase #2 $197.68   9.321%   $216.1058   $216.11   $216.10   $216.10  
  Purchase #3 $146.45   3.506%   $151.5845   $151.58   $151.60   $151.60  
  Purchase #4 $122.86   3.201%   $126.7927   $126.79   $126.80   $126.80  
  Purchase #5 $59.86   10.796%   $66.3225   $66.32   $66.30   $66.30  
  Purchase #6 $69.85   6.838%   $74.6263   $74.63   $74.65   $74.60  
  Purchase #7 $36.51   4.211%   $38.0474   $38.05   $38.05   $38.00  
  7 purchase totals = $680.98       $723.4910   $723.49   $723.50   $723.40