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 $31.89   4.269%   $33.2514   $33.25   $33.25   $33.30  
  Purchase #2 $186.53   3.441%   $192.9485   $192.95   $192.95   $192.90  
  Purchase #3 $126.86   4.771%   $132.9125   $132.91   $132.90   $132.90  
  Purchase #4 $56.29   11.869%   $62.9711   $62.97   $62.95   $63.00  
  Purchase #5 $184.44   13.149%   $208.692   $208.69   $208.70   $208.70  
  Purchase #6 $124.91   5.774%   $132.1223   $132.12   $132.10   $132.10  
  Purchase #7 $144.93   6.174%   $153.878   $153.88   $153.90   $153.90  
  7 purchase totals = $855.85       $916.7758   $916.77   $916.75   $916.80