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	$55.85	6.591%	$59.5311	$59.53	$59.55	$59.50
Purchase #2	$90.74	9.415%	$99.2832	$99.28	$99.30	$99.30
Purchase #3	$214.56	13.457%	$243.4333	$243.43	$243.45	$243.40
Purchase #4	$60.98	11.303%	$67.8726	$67.87	$67.85	$67.90
Purchase #5	$50.42	11.601%	$56.2692	$56.27	$56.25	$56.30
Purchase #6	$215.94	10.190%	$237.9443	$237.94	$237.95	$237.90
Purchase #7	$149.66	4.378%	$156.2121	$156.21	$156.20	$156.20
7 purchase totals =	$838.15		$920.5458	$920.53	$920.55	$920.50