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 $9.97   6.625%   $10.6305   $10.63   $10.65   $10.60  
  Purchase #2 $215.33   8.175%   $232.9332   $232.93   $232.95   $232.90  
  Purchase #3 $36.94   11.144%   $41.0566   $41.06   $41.05   $41.10  
  Purchase #4 $226.96   4.744%   $237.727   $237.73   $237.75   $237.70  
  Purchase #5 $70.58   3.516%   $73.0616   $73.06   $73.05   $73.10  
  Purchase #6 $49.47   7.747%   $53.3024   $53.30   $53.30   $53.30  
  Purchase #7 $73.68   4.777%   $77.1997   $77.20   $77.20   $77.20  
  7 purchase totals = $682.93       $725.9110   $725.91   $725.95   $725.90