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 $70.25   5.303%   $73.9754   $73.98   $74.00   $74.00  
  Purchase #2 $97.61   3.373%   $100.9024   $100.90   $100.90   $100.90  
  Purchase #3 $11.46   6.779%   $12.2369   $12.24   $12.25   $12.20  
  Purchase #4 $79.73   3.635%   $82.6282   $82.63   $82.65   $82.60  
  Purchase #5 $149.50   3.388%   $154.5651   $154.57   $154.55   $154.60  
  Purchase #6 $192.51   7.505%   $206.9579   $206.96   $206.95   $207.00  
  Purchase #7 $201.81   9.695%   $221.3755   $221.38   $221.40   $221.40  
  7 purchase totals = $802.87       $852.6414   $852.66   $852.70   $852.70