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	$222.72	12.631%	$250.8518	$250.85	$250.85	$250.90
Purchase #2	$89.65	10.681%	$99.2255	$99.23	$99.25	$99.20
Purchase #3	$67.74	5.426%	$71.4156	$71.42	$71.40	$71.40
Purchase #4	$206.64	4.411%	$215.7549	$215.75	$215.75	$215.80
Purchase #5	$86.50	11.491%	$96.4397	$96.44	$96.45	$96.40
Purchase #6	$58.58	6.209%	$62.2172	$62.22	$62.20	$62.20
Purchase #7	$65.48	6.439%	$69.6963	$69.70	$69.70	$69.70
7 purchase totals =	$797.31		$865.6010	$865.61	$865.60	$865.60