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	$91.45	10.341%	$100.9068	$100.91	$100.90	$100.90
Purchase #2	$136.87	3.190%	$141.2362	$141.24	$141.25	$141.20
Purchase #3	$87.98	5.223%	$92.5752	$92.58	$92.60	$92.60
Purchase #4	$163.88	12.718%	$184.7223	$184.72	$184.70	$184.70
Purchase #5	$110.49	4.300%	$115.2411	$115.24	$115.25	$115.20
Purchase #6	$33.61	12.763%	$37.8996	$37.90	$37.90	$37.90
Purchase #7	$142.58	9.766%	$156.5044	$156.50	$156.50	$156.50
7 purchase totals =	$766.86		$829.0856	$829.09	$829.10	$829.00