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	$86.28	4.487%	$90.1514	$90.15	$90.15	$90.20
Purchase #2	$227.40	13.838%	$258.8676	$258.87	$258.85	$258.90
Purchase #3	$180.99	8.514%	$196.3995	$196.40	$196.40	$196.40
Purchase #4	$235.73	12.123%	$264.3075	$264.31	$264.30	$264.30
Purchase #5	$148.62	13.580%	$168.8026	$168.80	$168.80	$168.80
Purchase #6	$238.88	5.441%	$251.8775	$251.88	$251.90	$251.90
Purchase #7	$122.88	9.142%	$134.1137	$134.11	$134.10	$134.10
7 purchase totals =	$1,240.78		$1,364.5198	$1,364.52	$1,364.50	$1,364.60