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	$19.72	5.129%	$20.7314	$20.73	$20.75	$20.70
Purchase #2	$125.95	12.836%	$142.1169	$142.12	$142.10	$142.10
Purchase #3	$162.28	10.472%	$179.274	$179.27	$179.25	$179.30
Purchase #4	$30.25	9.423%	$33.1005	$33.10	$33.10	$33.10
Purchase #5	$181.78	4.112%	$189.2548	$189.25	$189.25	$189.30
Purchase #6	$48.84	4.163%	$50.8732	$50.87	$50.85	$50.90
Purchase #7	$195.83	6.308%	$208.183	$208.18	$208.20	$208.20
7 purchase totals =	$764.65		$823.5338	$823.52	$823.50	$823.60