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	$163.78	11.862%	$183.2076	$183.21	$183.20	$183.20
Purchase #2	$152.54	3.723%	$158.2191	$158.22	$158.20	$158.20
Purchase #3	$6.56	4.347%	$6.8452	$6.85	$6.85	$6.80
Purchase #4	$61.64	13.831%	$70.1654	$70.17	$70.15	$70.20
Purchase #5	$45.74	10.451%	$50.5203	$50.52	$50.50	$50.50
Purchase #6	$67.53	4.139%	$70.3251	$70.33	$70.35	$70.30
Purchase #7	$55.56	10.751%	$61.5333	$61.53	$61.55	$61.50
7 purchase totals =	$553.35		$600.8160	$600.83	$600.80	$600.70