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 $131.75   11.117%   $146.3966   $146.40   $146.40   $146.40  
  Purchase #2 $222.72   3.109%   $229.6444   $229.64   $229.65   $229.60  
  Purchase #3 $220.83   12.702%   $248.8798   $248.88   $248.90   $248.90  
  Purchase #4 $229.88   8.474%   $249.36   $249.36   $249.35   $249.40  
  Purchase #5 $64.61   10.555%   $71.4296   $71.43   $71.45   $71.40  
  Purchase #6 $186.35   13.370%   $211.265   $211.27   $211.25   $211.30  
  Purchase #7 $76.84   10.245%   $84.7123   $84.71   $84.70   $84.70  
  7 purchase totals = $1,132.98       $1,241.6877   $1,241.69   $1,241.70   $1,241.70