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 $65.42   12.399%   $73.5314   $73.53   $73.55   $73.50  
  Purchase #2 $32.58   6.794%   $34.7935   $34.79   $34.80   $34.80  
  Purchase #3 $130.94   5.109%   $137.6297   $137.63   $137.65   $137.60  
  Purchase #4 $250.48   8.662%   $272.1766   $272.18   $272.20   $272.20  
  Purchase #5 $118.25   4.388%   $123.4388   $123.44   $123.45   $123.40  
  Purchase #6 $178.48   8.740%   $194.0792   $194.08   $194.10   $194.10  
  Purchase #7 $145.85   5.738%   $154.2189   $154.22   $154.20   $154.20  
  7 purchase totals = $922.00       $989.8681   $989.87   $989.95   $989.80