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	$17.66	6.433%	$18.7961	$18.80	$18.80	$18.80
Purchase #2	$225.95	5.533%	$238.4518	$238.45	$238.45	$238.50
Purchase #3	$244.65	7.619%	$263.2899	$263.29	$263.30	$263.30
Purchase #4	$117.79	11.649%	$131.5114	$131.51	$131.50	$131.50
Purchase #5	$91.93	4.781%	$96.3252	$96.33	$96.35	$96.30
Purchase #6	$85.92	4.130%	$89.4685	$89.47	$89.45	$89.50
Purchase #7	$213.69	5.843%	$226.1759	$226.18	$226.20	$226.20
7 purchase totals =	$997.59		$1,064.0188	$1,064.03	$1,064.05	$1,064.10