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 $102.90   10.772%   $113.9844   $113.98   $114.00   $114.00  
  Purchase #2 $23.95   13.574%   $27.201   $27.20   $27.20   $27.20  
  Purchase #3 $83.83   8.594%   $91.0344   $91.03   $91.05   $91.00  
  Purchase #4 $26.40   5.870%   $27.9497   $27.95   $27.95   $27.90  
  Purchase #5 $51.42   10.142%   $56.635   $56.64   $56.65   $56.60  
  Purchase #6 $48.99   6.556%   $52.2018   $52.20   $52.20   $52.20  
  Purchase #7 $7.35   5.623%   $7.7633   $7.76   $7.75   $7.80  
  7 purchase totals = $344.84       $376.7696   $376.76   $376.80   $376.70