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	$66.69	5.232%	$70.1792	$70.18	$70.20	$70.20
Purchase #2	$53.88	10.124%	$59.3348	$59.33	$59.35	$59.30
Purchase #3	$47.77	12.815%	$53.8917	$53.89	$53.90	$53.90
Purchase #4	$73.62	11.359%	$81.9825	$81.98	$82.00	$82.00
Purchase #5	$227.78	12.517%	$256.2912	$256.29	$256.30	$256.30
Purchase #6	$167.71	4.774%	$175.7165	$175.72	$175.70	$175.70
Purchase #7	$99.58	7.729%	$107.2765	$107.28	$107.30	$107.30
7 purchase totals =	$737.03		$804.6724	$804.67	$804.75	$804.70