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 $77.76   7.214%   $83.3696   $83.37   $83.35   $83.40  
  Purchase #2 $114.77   10.866%   $127.2409   $127.24   $127.25   $127.20  
  Purchase #3 $223.72   4.161%   $233.029   $233.03   $233.05   $233.00  
  Purchase #4 $177.56   10.526%   $196.25   $196.25   $196.25   $196.30  
  Purchase #5 $15.26   6.531%   $16.2566   $16.26   $16.25   $16.30  
  Purchase #6 $150.53   7.842%   $162.3346   $162.33   $162.35   $162.30  
  Purchase #7 $174.97   10.599%   $193.5151   $193.52   $193.50   $193.50  
  7 purchase totals = $934.57       $1,011.9958   $1,012.00   $1,012.00   $1,012.00