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 $90.42   8.356%   $97.9755   $97.98   $98.00   $98.00  
  Purchase #2 $184.69   11.871%   $206.6145   $206.61   $206.60   $206.60  
  Purchase #3 $106.50   7.753%   $114.7569   $114.76   $114.75   $114.80  
  Purchase #4 $52.81   4.827%   $55.3591   $55.36   $55.35   $55.40  
  Purchase #5 $202.29   11.583%   $225.7213   $225.72   $225.70   $225.70  
  Purchase #6 $207.64   6.808%   $221.7761   $221.78   $221.80   $221.80  
  Purchase #7 $124.65   4.722%   $130.536   $130.54   $130.55   $130.50  
  7 purchase totals = $969.00       $1,052.7394   $1,052.75   $1,052.75   $1,052.80