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	$111.51	3.650%	$115.5801	$115.58	$115.60	$115.60
Purchase #2	$221.38	7.796%	$238.6388	$238.64	$238.65	$238.60
Purchase #3	$123.49	5.856%	$130.7216	$130.72	$130.70	$130.70
Purchase #4	$220.41	13.390%	$249.9229	$249.92	$249.90	$249.90
Purchase #5	$59.80	7.294%	$64.1618	$64.16	$64.15	$64.20
Purchase #6	$36.34	4.496%	$37.9738	$37.97	$37.95	$38.00
Purchase #7	$225.41	13.540%	$255.9305	$255.93	$255.95	$255.90
7 purchase totals =	$998.34		$1,092.9295	$1,092.92	$1,092.90	$1,092.90