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 $246.28   5.582%   $260.0273   $260.03   $260.05   $260.00  
  Purchase #2 $240.55   12.679%   $271.0493   $271.05   $271.05   $271.00  
  Purchase #3 $5.35   6.545%   $5.7002   $5.70   $5.70   $5.70  
  Purchase #4 $53.59   13.670%   $60.9158   $60.92   $60.90   $60.90  
  Purchase #5 $120.49   5.740%   $127.4061   $127.41   $127.40   $127.40  
  Purchase #6 $69.49   11.745%   $77.6516   $77.65   $77.65   $77.70  
  Purchase #7 $98.63   3.670%   $102.2497   $102.25   $102.25   $102.20  
  7 purchase totals = $834.38       $905.0000   $905.01   $905.00   $904.90