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 $180.81   8.294%   $195.8064   $195.81   $195.80   $195.80  
  Purchase #2 $191.26   6.265%   $203.2424   $203.24   $203.25   $203.20  
  Purchase #3 $124.50   6.337%   $132.3896   $132.39   $132.40   $132.40  
  Purchase #4 $221.67   12.371%   $249.0928   $249.09   $249.10   $249.10  
  Purchase #5 $43.87   10.380%   $48.4237   $48.42   $48.40   $48.40  
  Purchase #6 $34.55   3.614%   $35.7986   $35.80   $35.80   $35.80  
  Purchase #7 $140.69   13.276%   $159.368   $159.37   $159.35   $159.40  
  7 purchase totals = $937.35       $1,024.1215   $1,024.12   $1,024.10   $1,024.10