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	$234.79	12.550%	$264.2561	$264.26	$264.25	$264.30
Purchase #2	$129.79	11.732%	$145.017	$145.02	$145.00	$145.00
Purchase #3	$27.56	8.653%	$29.9448	$29.94	$29.95	$29.90
Purchase #4	$174.72	12.449%	$196.4709	$196.47	$196.45	$196.50
Purchase #5	$126.62	12.659%	$142.6488	$142.65	$142.65	$142.60
Purchase #6	$67.70	4.465%	$70.7228	$70.72	$70.70	$70.70
Purchase #7	$37.25	12.521%	$41.9141	$41.91	$41.90	$41.90
7 purchase totals =	$798.43		$890.9745	$890.97	$890.90	$890.90