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	$229.72	5.120%	$241.4817	$241.48	$241.50	$241.50
Purchase #2	$80.93	11.104%	$89.9165	$89.92	$89.90	$89.90
Purchase #3	$236.44	11.472%	$263.5644	$263.56	$263.55	$263.60
Purchase #4	$7.78	13.771%	$8.8514	$8.85	$8.85	$8.90
Purchase #5	$79.38	8.133%	$85.836	$85.84	$85.85	$85.80
Purchase #6	$189.68	9.376%	$207.4644	$207.46	$207.45	$207.50
Purchase #7	$105.27	6.873%	$112.5052	$112.51	$112.50	$112.50
7 purchase totals =	$929.20		$1,009.6196	$1,009.62	$1,009.60	$1,009.70