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 $167.71   12.556%   $188.7677   $188.77   $188.75   $188.80  
  Purchase #2 $99.53   7.765%   $107.2585   $107.26   $107.25   $107.30  
  Purchase #3 $234.69   12.472%   $263.9605   $263.96   $263.95   $264.00  
  Purchase #4 $5.48   3.322%   $5.662   $5.66   $5.65   $5.70  
  Purchase #5 $240.47   9.224%   $262.651   $262.65   $262.65   $262.70  
  Purchase #6 $30.55   3.220%   $31.5337   $31.53   $31.55   $31.50  
  Purchase #7 $101.35   8.463%   $109.9273   $109.93   $109.95   $109.90  
  7 purchase totals = $879.78       $969.7607   $969.76   $969.75   $969.90