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 $116.44   8.617%   $126.4736   $126.47   $126.45   $126.50  
  Purchase #2 $10.56   6.499%   $11.2463   $11.25   $11.25   $11.20  
  Purchase #3 $222.43   11.527%   $248.0695   $248.07   $248.05   $248.10  
  Purchase #4 $106.97   4.827%   $112.1334   $112.13   $112.15   $112.10  
  Purchase #5 $194.57   12.236%   $218.3776   $218.38   $218.40   $218.40  
  Purchase #6 $73.76   5.619%   $77.9046   $77.90   $77.90   $77.90  
  Purchase #7 $155.27   10.657%   $171.8171   $171.82   $171.80   $171.80  
  7 purchase totals = $880.00       $966.0221   $966.02   $966.00   $966.00