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	$199.82	3.681%	$207.1754	$207.18	$207.20	$207.20
Purchase #2	$221.33	11.772%	$247.385	$247.39	$247.40	$247.40
Purchase #3	$123.84	13.557%	$140.629	$140.63	$140.65	$140.60
Purchase #4	$99.62	4.339%	$103.9425	$103.94	$103.95	$103.90
Purchase #5	$99.61	8.576%	$108.1526	$108.15	$108.15	$108.20
Purchase #6	$111.74	10.722%	$123.7208	$123.72	$123.70	$123.70
Purchase #7	$131.40	7.162%	$140.8109	$140.81	$140.80	$140.80
7 purchase totals =	$987.36		$1,071.8162	$1,071.82	$1,071.85	$1,071.80