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 $216.66   9.855%   $238.0118   $238.01   $238.00   $238.00  
  Purchase #2 $214.99   12.500%   $241.8638   $241.86   $241.85   $241.90  
  Purchase #3 $49.58   3.409%   $51.2702   $51.27   $51.25   $51.30  
  Purchase #4 $206.26   3.570%   $213.6235   $213.62   $213.60   $213.60  
  Purchase #5 $84.65   5.331%   $89.1627   $89.16   $89.15   $89.20  
  Purchase #6 $237.37   12.401%   $266.8063   $266.81   $266.80   $266.80  
  Purchase #7 $54.67   10.655%   $60.4951   $60.50   $60.50   $60.50  
  7 purchase totals = $1,064.18       $1,161.2334   $1,161.23   $1,161.15   $1,161.30