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 $78.46   10.793%   $86.9282   $86.93   $86.95   $86.90  
  Purchase #2 $85.53   13.479%   $97.0586   $97.06   $97.05   $97.10  
  Purchase #3 $85.62   7.293%   $91.8643   $91.86   $91.85   $91.90  
  Purchase #4 $53.44   13.162%   $60.4738   $60.47   $60.45   $60.50  
  Purchase #5 $66.84   5.836%   $70.7408   $70.74   $70.75   $70.70  
  Purchase #6 $244.83   3.207%   $252.6817   $252.68   $252.70   $252.70  
  Purchase #7 $100.44   4.349%   $104.8081   $104.81   $104.80   $104.80  
  7 purchase totals = $715.16       $764.5555   $764.55   $764.55   $764.60