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	$7.36	13.428%	$8.3483	$8.35	$8.35	$8.30
Purchase #2	$221.26	12.773%	$249.5215	$249.52	$249.50	$249.50
Purchase #3	$139.59	3.539%	$144.5301	$144.53	$144.55	$144.50
Purchase #4	$30.55	10.511%	$33.7611	$33.76	$33.75	$33.80
Purchase #5	$88.82	4.552%	$92.8631	$92.86	$92.85	$92.90
Purchase #6	$19.51	8.335%	$21.1362	$21.14	$21.15	$21.10
Purchase #7	$13.77	3.256%	$14.2184	$14.22	$14.20	$14.20
7 purchase totals =	$520.86		$564.3787	$564.38	$564.35	$564.30