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	$82.32	8.742%	$89.5164	$89.52	$89.50	$89.50
Purchase #2	$219.71	12.630%	$247.4594	$247.46	$247.45	$247.50
Purchase #3	$67.41	11.423%	$75.1102	$75.11	$75.10	$75.10
Purchase #4	$172.57	4.198%	$179.8145	$179.81	$179.80	$179.80
Purchase #5	$39.90	12.312%	$44.8125	$44.81	$44.80	$44.80
Purchase #6	$153.52	5.819%	$162.4533	$162.45	$162.45	$162.50
Purchase #7	$42.71	4.714%	$44.7233	$44.72	$44.70	$44.70
7 purchase totals =	$778.14		$843.8896	$843.88	$843.80	$843.90