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 $156.37   6.823%   $167.0391   $167.04   $167.05   $167.00  
  Purchase #2 $47.28   12.855%   $53.3578   $53.36   $53.35   $53.40  
  Purchase #3 $191.91   13.442%   $217.7065   $217.71   $217.70   $217.70  
  Purchase #4 $217.36   4.383%   $226.8869   $226.89   $226.90   $226.90  
  Purchase #5 $11.26   9.608%   $12.3419   $12.34   $12.35   $12.30  
  Purchase #6 $53.90   13.209%   $61.0197   $61.02   $61.00   $61.00  
  Purchase #7 $137.44   7.676%   $147.9899   $147.99   $148.00   $148.00  
  7 purchase totals = $815.52       $886.3418   $886.35   $886.35   $886.30