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	$155.59	7.259%	$166.8843	$166.88	$166.90	$166.90
Purchase #2	$115.79	10.455%	$127.8958	$127.90	$127.90	$127.90
Purchase #3	$162.56	3.377%	$168.0497	$168.05	$168.05	$168.00
Purchase #4	$82.39	10.633%	$91.1505	$91.15	$91.15	$91.20
Purchase #5	$102.58	8.328%	$111.1229	$111.12	$111.10	$111.10
Purchase #6	$176.75	4.414%	$184.5517	$184.55	$184.55	$184.60
Purchase #7	$119.89	7.698%	$129.1191	$129.12	$129.10	$129.10
7 purchase totals =	$915.55		$978.7740	$978.77	$978.75	$978.80