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 $240.88   5.688%   $254.5813   $254.58   $254.60   $254.60  
  Purchase #2 $182.90   9.667%   $200.5809   $200.58   $200.60   $200.60  
  Purchase #3 $182.27   5.641%   $192.5519   $192.55   $192.55   $192.60  
  Purchase #4 $236.66   3.503%   $244.9502   $244.95   $244.95   $245.00  
  Purchase #5 $59.30   7.589%   $63.8003   $63.80   $63.80   $63.80  
  Purchase #6 $213.54   9.723%   $234.3025   $234.30   $234.30   $234.30  
  Purchase #7 $64.68   10.601%   $71.5367   $71.54   $71.55   $71.50  
  7 purchase totals = $1,180.23       $1,262.3038   $1,262.30   $1,262.35   $1,262.40