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	$28.89	9.130%	$31.5277	$31.53	$31.55	$31.50
Purchase #2	$74.37	5.700%	$78.6091	$78.61	$78.60	$78.60
Purchase #3	$215.38	9.141%	$235.0679	$235.07	$235.05	$235.10
Purchase #4	$239.87	4.813%	$251.4149	$251.41	$251.40	$251.40
Purchase #5	$88.62	7.534%	$95.2966	$95.30	$95.30	$95.30
Purchase #6	$141.93	8.625%	$154.1715	$154.17	$154.15	$154.20
Purchase #7	$149.73	13.543%	$170.0079	$170.01	$170.00	$170.00
7 purchase totals =	$938.79		$1,016.0956	$1,016.10	$1,016.05	$1,016.10