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 $61.25   3.803%   $63.5793   $63.58   $63.60   $63.60  
  Purchase #2 $53.88   13.206%   $60.9954   $61.00   $61.00   $61.00  
  Purchase #3 $172.25   3.458%   $178.2064   $178.21   $178.20   $178.20  
  Purchase #4 $235.94   13.668%   $268.1883   $268.19   $268.20   $268.20  
  Purchase #5 $199.89   7.762%   $215.4055   $215.41   $215.40   $215.40  
  Purchase #6 $5.26   10.847%   $5.8306   $5.83   $5.85   $5.80  
  Purchase #7 $15.88   13.433%   $18.0132   $18.01   $18.00   $18.00  
  7 purchase totals = $744.35       $810.2187   $810.23   $810.25   $810.20