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	$83.56	3.708%	$86.6584	$86.66	$86.65	$86.70
Purchase #2	$179.94	9.297%	$196.669	$196.67	$196.65	$196.70
Purchase #3	$119.59	4.803%	$125.3339	$125.33	$125.35	$125.30
Purchase #4	$38.33	10.570%	$42.3815	$42.38	$42.40	$42.40
Purchase #5	$162.52	5.705%	$171.7918	$171.79	$171.80	$171.80
Purchase #6	$79.31	11.354%	$88.3149	$88.31	$88.30	$88.30
Purchase #7	$101.89	12.348%	$114.4714	$114.47	$114.45	$114.50
7 purchase totals =	$765.14		$825.6209	$825.61	$825.60	$825.70