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	$52.38	9.830%	$57.529	$57.53	$57.55	$57.50
Purchase #2	$159.29	7.337%	$170.9771	$170.98	$171.00	$171.00
Purchase #3	$120.78	5.343%	$127.2333	$127.23	$127.25	$127.20
Purchase #4	$82.77	7.293%	$88.8064	$88.81	$88.80	$88.80
Purchase #5	$165.62	8.406%	$179.542	$179.54	$179.55	$179.50
Purchase #6	$207.89	3.140%	$214.4177	$214.42	$214.40	$214.40
Purchase #7	$218.58	7.115%	$234.132	$234.13	$234.15	$234.10
7 purchase totals =	$1,007.31		$1,072.6375	$1,072.64	$1,072.70	$1,072.50