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 $199.58   9.246%   $218.0332   $218.03   $218.05   $218.00  
  Purchase #2 $157.88   12.190%   $177.1256   $177.13   $177.15   $177.10  
  Purchase #3 $107.96   4.296%   $112.598   $112.60   $112.60   $112.60  
  Purchase #4 $175.80   11.864%   $196.6569   $196.66   $196.65   $196.70  
  Purchase #5 $50.82   10.697%   $56.2562   $56.26   $56.25   $56.30  
  Purchase #6 $213.90   5.153%   $224.9223   $224.92   $224.90   $224.90  
  Purchase #7 $56.33   11.814%   $62.9848   $62.98   $63.00   $63.00  
  7 purchase totals = $962.27       $1,048.5770   $1,048.58   $1,048.60   $1,048.60