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	$55.58	3.365%	$57.4503	$57.45	$57.45	$57.50
Purchase #2	$51.67	3.797%	$53.6319	$53.63	$53.65	$53.60
Purchase #3	$199.38	8.137%	$215.6036	$215.60	$215.60	$215.60
Purchase #4	$223.55	10.720%	$247.5146	$247.51	$247.50	$247.50
Purchase #5	$61.62	9.514%	$67.4825	$67.48	$67.50	$67.50
Purchase #6	$57.86	11.497%	$64.5122	$64.51	$64.50	$64.50
Purchase #7	$79.62	3.765%	$82.6177	$82.62	$82.60	$82.60
7 purchase totals =	$729.28		$788.8128	$788.80	$788.80	$788.80