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	$78.97	13.469%	$89.6065	$89.61	$89.60	$89.60
Purchase #2	$165.79	4.192%	$172.7399	$172.74	$172.75	$172.70
Purchase #3	$222.50	6.119%	$236.1148	$236.11	$236.10	$236.10
Purchase #4	$250.27	11.184%	$278.2602	$278.26	$278.25	$278.30
Purchase #5	$71.79	9.205%	$78.3983	$78.40	$78.40	$78.40
Purchase #6	$102.45	7.483%	$110.1163	$110.12	$110.10	$110.10
Purchase #7	$77.49	13.827%	$88.2045	$88.20	$88.20	$88.20
7 purchase totals =	$969.26		$1,053.4405	$1,053.44	$1,053.40	$1,053.40