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	$172.25	12.752%	$194.2153	$194.22	$194.20	$194.20
Purchase #2	$59.49	10.354%	$65.6496	$65.65	$65.65	$65.60
Purchase #3	$131.58	12.754%	$148.3617	$148.36	$148.35	$148.40
Purchase #4	$60.85	7.259%	$65.2671	$65.27	$65.25	$65.30
Purchase #5	$54.49	5.454%	$57.4619	$57.46	$57.45	$57.50
Purchase #6	$201.90	9.417%	$220.9129	$220.91	$220.90	$220.90
Purchase #7	$86.33	4.681%	$90.3711	$90.37	$90.35	$90.40
7 purchase totals =	$766.89		$842.2396	$842.24	$842.15	$842.30