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 $173.72   12.583%   $195.5792   $195.58   $195.60   $195.60  
  Purchase #2 $60.78   12.287%   $68.248   $68.25   $68.25   $68.20  
  Purchase #3 $159.34   10.261%   $175.6899   $175.69   $175.70   $175.70  
  Purchase #4 $163.34   3.248%   $168.6453   $168.65   $168.65   $168.60  
  Purchase #5 $52.99   7.793%   $57.1195   $57.12   $57.10   $57.10  
  Purchase #6 $12.78   6.416%   $13.6   $13.60   $13.60   $13.60  
  Purchase #7 $213.81   12.274%   $240.053   $240.05   $240.05   $240.10  
  7 purchase totals = $836.76       $918.9349   $918.94   $918.95   $918.90