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	$191.70	10.864%	$212.5263	$212.53	$212.55	$212.50
Purchase #2	$97.29	7.638%	$104.721	$104.72	$104.70	$104.70
Purchase #3	$56.41	4.683%	$59.0517	$59.05	$59.05	$59.10
Purchase #4	$87.59	11.143%	$97.3502	$97.35	$97.35	$97.40
Purchase #5	$104.60	6.619%	$111.5235	$111.52	$111.50	$111.50
Purchase #6	$89.80	13.313%	$101.7551	$101.76	$101.75	$101.80
Purchase #7	$207.93	12.524%	$233.9712	$233.97	$233.95	$234.00
7 purchase totals =	$835.32		$920.8990	$920.90	$920.85	$921.00