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	$54.98	5.202%	$57.8401	$57.84	$57.85	$57.80
Purchase #2	$148.29	4.436%	$154.8681	$154.87	$154.85	$154.90
Purchase #3	$186.36	5.284%	$196.2073	$196.21	$196.20	$196.20
Purchase #4	$133.64	6.624%	$142.4923	$142.49	$142.50	$142.50
Purchase #5	$247.74	3.389%	$256.1359	$256.14	$256.15	$256.10
Purchase #6	$49.45	7.190%	$53.0055	$53.01	$53.00	$53.00
Purchase #7	$54.46	12.223%	$61.1166	$61.12	$61.10	$61.10
7 purchase totals =	$874.92		$921.6658	$921.68	$921.65	$921.60