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	$55.52	4.827%	$58.2	$58.20	$58.20	$58.20
Purchase #2	$50.91	11.700%	$56.8665	$56.87	$56.85	$56.90
Purchase #3	$152.62	12.118%	$171.1145	$171.11	$171.10	$171.10
Purchase #4	$99.68	3.568%	$103.2366	$103.24	$103.25	$103.20
Purchase #5	$162.68	10.403%	$179.6036	$179.60	$179.60	$179.60
Purchase #6	$42.62	7.582%	$45.8514	$45.85	$45.85	$45.90
Purchase #7	$61.87	8.545%	$67.1568	$67.16	$67.15	$67.20
7 purchase totals =	$625.90		$682.0294	$682.03	$682.00	$682.10