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 $208.70   10.818%   $231.2772   $231.28   $231.30   $231.30  
  Purchase #2 $161.36   10.110%   $177.6735   $177.67   $177.65   $177.70  
  Purchase #3 $61.71   10.552%   $68.2216   $68.22   $68.20   $68.20  
  Purchase #4 $87.36   11.653%   $97.5401   $97.54   $97.55   $97.50  
  Purchase #5 $146.36   12.232%   $164.2628   $164.26   $164.25   $164.30  
  Purchase #6 $157.27   3.515%   $162.798   $162.80   $162.80   $162.80  
  Purchase #7 $185.97   12.264%   $208.7774   $208.78   $208.80   $208.80  
  7 purchase totals = $1,008.73       $1,110.5506   $1,110.55   $1,110.55   $1,110.60