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	$116.59	10.516%	$128.8506	$128.85	$128.85	$128.90
Purchase #2	$146.76	7.437%	$157.6745	$157.67	$157.65	$157.70
Purchase #3	$16.97	6.771%	$18.119	$18.12	$18.10	$18.10
Purchase #4	$91.26	9.705%	$100.1168	$100.12	$100.10	$100.10
Purchase #5	$35.29	4.241%	$36.7866	$36.79	$36.80	$36.80
Purchase #6	$137.86	3.323%	$142.4411	$142.44	$142.45	$142.40
Purchase #7	$209.56	4.457%	$218.9001	$218.90	$218.90	$218.90
7 purchase totals =	$754.29		$802.8887	$802.89	$802.85	$802.90