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 $161.76   13.726%   $183.9632   $183.96   $183.95   $184.00  
  Purchase #2 $173.25   6.831%   $185.0847   $185.08   $185.10   $185.10  
  Purchase #3 $96.98   11.229%   $107.8699   $107.87   $107.85   $107.90  
  Purchase #4 $137.92   12.312%   $154.9007   $154.90   $154.90   $154.90  
  Purchase #5 $185.77   5.665%   $196.2939   $196.29   $196.30   $196.30  
  Purchase #6 $157.84   12.706%   $177.8952   $177.90   $177.90   $177.90  
  Purchase #7 $114.30   6.127%   $121.3032   $121.30   $121.30   $121.30  
  7 purchase totals = $1,027.82       $1,127.3108   $1,127.30   $1,127.30   $1,127.40