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 $125.82   11.704%   $140.546   $140.55   $140.55   $140.50  
  Purchase #2 $23.49   13.230%   $26.5977   $26.60   $26.60   $26.60  
  Purchase #3 $12.67   13.408%   $14.3688   $14.37   $14.35   $14.40  
  Purchase #4 $209.68   4.690%   $219.514   $219.51   $219.50   $219.50  
  Purchase #5 $213.82   5.818%   $226.26   $226.26   $226.25   $226.30  
  Purchase #6 $137.98   13.700%   $156.8833   $156.88   $156.90   $156.90  
  Purchase #7 $92.89   11.162%   $103.2584   $103.26   $103.25   $103.30  
  7 purchase totals = $816.35       $887.4282   $887.43   $887.40   $887.50