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 $180.35   8.241%   $195.2126   $195.21   $195.20   $195.20  
  Purchase #2 $112.97   12.690%   $127.3059   $127.31   $127.30   $127.30  
  Purchase #3 $61.50   6.122%   $65.265   $65.27   $65.25   $65.30  
  Purchase #4 $173.68   11.360%   $193.41   $193.41   $193.40   $193.40  
  Purchase #5 $94.39   3.672%   $97.856   $97.86   $97.85   $97.90  
  Purchase #6 $194.47   7.242%   $208.5535   $208.55   $208.55   $208.60  
  Purchase #7 $225.74   10.652%   $249.7858   $249.79   $249.80   $249.80  
  7 purchase totals = $1,043.10       $1,137.3888   $1,137.40   $1,137.35   $1,137.50