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 $162.70   13.407%   $184.5132   $184.51   $184.50   $184.50  
  Purchase #2 $23.55   11.631%   $26.2891   $26.29   $26.30   $26.30  
  Purchase #3 $158.66   9.805%   $174.2166   $174.22   $174.20   $174.20  
  Purchase #4 $38.78   5.786%   $41.0238   $41.02   $41.00   $41.00  
  Purchase #5 $33.37   3.252%   $34.4552   $34.46   $34.45   $34.50  
  Purchase #6 $48.39   8.839%   $52.6672   $52.67   $52.65   $52.70  
  Purchase #7 $147.25   11.134%   $163.6448   $163.64   $163.65   $163.60  
  7 purchase totals = $612.70       $676.8099   $676.81   $676.75   $676.80