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 $74.64   10.234%   $82.2787   $82.28   $82.30   $82.30  
  Purchase #2 $154.96   13.739%   $176.25   $176.25   $176.25   $176.30  
  Purchase #3 $91.29   7.737%   $98.3531   $98.35   $98.35   $98.40  
  Purchase #4 $219.92   9.771%   $241.4084   $241.41   $241.40   $241.40  
  Purchase #5 $97.26   4.397%   $101.5365   $101.54   $101.55   $101.50  
  Purchase #6 $144.32   10.686%   $159.742   $159.74   $159.75   $159.70  
  Purchase #7 $60.91   10.157%   $67.0966   $67.10   $67.10   $67.10  
  7 purchase totals = $843.30       $926.6653   $926.67   $926.70   $926.70