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	$19.92	4.732%	$20.8626	$20.86	$20.85	$20.90
Purchase #2	$209.36	9.609%	$229.4774	$229.48	$229.50	$229.50
Purchase #3	$137.52	3.129%	$141.823	$141.82	$141.80	$141.80
Purchase #4	$118.75	7.469%	$127.6194	$127.62	$127.60	$127.60
Purchase #5	$126.94	3.139%	$130.9246	$130.92	$130.90	$130.90
Purchase #6	$78.30	9.478%	$85.7213	$85.72	$85.70	$85.70
Purchase #7	$144.79	3.572%	$149.9619	$149.96	$149.95	$150.00
7 purchase totals =	$835.58		$886.3902	$886.38	$886.30	$886.40