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 $60.63   8.788%   $65.9582   $65.96   $65.95   $66.00  
  Purchase #2 $144.57   11.691%   $161.4717   $161.47   $161.45   $161.50  
  Purchase #3 $65.34   6.679%   $69.7041   $69.70   $69.70   $69.70  
  Purchase #4 $224.72   11.852%   $251.3538   $251.35   $251.35   $251.40  
  Purchase #5 $200.64   3.627%   $207.9172   $207.92   $207.90   $207.90  
  Purchase #6 $34.93   13.751%   $39.7332   $39.73   $39.75   $39.70  
  Purchase #7 $34.67   3.674%   $35.9438   $35.94   $35.95   $35.90  
  7 purchase totals = $765.50       $832.0820   $832.07   $832.05   $832.10