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	$91.58	11.189%	$101.8269	$101.83	$101.85	$101.80
Purchase #2	$241.46	13.123%	$273.1468	$273.15	$273.15	$273.10
Purchase #3	$223.27	7.230%	$239.4124	$239.41	$239.40	$239.40
Purchase #4	$100.91	8.515%	$109.5025	$109.50	$109.50	$109.50
Purchase #5	$173.75	10.130%	$191.3509	$191.35	$191.35	$191.40
Purchase #6	$250.59	3.776%	$260.0523	$260.05	$260.05	$260.10
Purchase #7	$158.93	4.793%	$166.5475	$166.55	$166.55	$166.50
7 purchase totals =	$1,240.49		$1,341.8393	$1,341.84	$1,341.85	$1,341.80