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	$222.95	11.842%	$249.3517	$249.35	$249.35	$249.40
Purchase #2	$156.66	7.417%	$168.2795	$168.28	$168.30	$168.30
Purchase #3	$54.42	3.402%	$56.2714	$56.27	$56.25	$56.30
Purchase #4	$5.93	4.178%	$6.1778	$6.18	$6.20	$6.20
Purchase #5	$89.76	10.569%	$99.2467	$99.25	$99.25	$99.20
Purchase #6	$19.30	9.428%	$21.1196	$21.12	$21.10	$21.10
Purchase #7	$54.83	7.623%	$59.0097	$59.01	$59.00	$59.00
7 purchase totals =	$603.85		$659.4564	$659.46	$659.45	$659.50