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 $61.32   8.757%   $66.6898   $66.69   $66.70   $66.70  
  Purchase #2 $47.78   3.665%   $49.5311   $49.53   $49.55   $49.50  
  Purchase #3 $22.77   13.220%   $25.7802   $25.78   $25.80   $25.80  
  Purchase #4 $196.51   10.617%   $217.3735   $217.37   $217.35   $217.40  
  Purchase #5 $27.26   12.551%   $30.6814   $30.68   $30.70   $30.70  
  Purchase #6 $248.33   6.695%   $264.9557   $264.96   $264.95   $265.00  
  Purchase #7 $242.35   8.524%   $263.0079   $263.01   $263.00   $263.00  
  7 purchase totals = $846.32       $918.0196   $918.02   $918.05   $918.10