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	$109.35	6.300%	$116.2391	$116.24	$116.25	$116.20
Purchase #2	$75.42	5.453%	$79.5327	$79.53	$79.55	$79.50
Purchase #3	$72.86	9.679%	$79.9121	$79.91	$79.90	$79.90
Purchase #4	$202.93	6.772%	$216.6724	$216.67	$216.65	$216.70
Purchase #5	$239.78	3.660%	$248.5559	$248.56	$248.55	$248.60
Purchase #6	$100.78	10.612%	$111.4748	$111.47	$111.45	$111.50
Purchase #7	$5.77	11.492%	$6.4331	$6.43	$6.45	$6.40
7 purchase totals =	$806.89		$858.8201	$858.81	$858.80	$858.80