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	$45.75	11.438%	$50.9829	$50.98	$51.00	$51.00
Purchase #2	$96.91	3.718%	$100.5131	$100.51	$100.50	$100.50
Purchase #3	$207.89	3.768%	$215.7233	$215.72	$215.70	$215.70
Purchase #4	$107.34	12.329%	$120.5739	$120.57	$120.55	$120.60
Purchase #5	$92.28	5.552%	$97.4034	$97.40	$97.40	$97.40
Purchase #6	$132.40	9.732%	$145.2852	$145.29	$145.30	$145.30
Purchase #7	$94.64	5.644%	$99.9815	$99.98	$100.00	$100.00
7 purchase totals =	$777.21		$830.4633	$830.45	$830.45	$830.50