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	$159.78	7.197%	$171.2794	$171.28	$171.30	$171.30
Purchase #2	$77.82	3.389%	$80.4573	$80.46	$80.45	$80.50
Purchase #3	$175.43	7.353%	$188.3294	$188.33	$188.35	$188.30
Purchase #4	$147.59	12.586%	$166.1657	$166.17	$166.15	$166.20
Purchase #5	$172.56	12.555%	$194.2249	$194.22	$194.20	$194.20
Purchase #6	$5.82	5.568%	$6.1441	$6.14	$6.15	$6.10
Purchase #7	$214.30	12.520%	$241.1304	$241.13	$241.15	$241.10
7 purchase totals =	$953.30		$1,047.7312	$1,047.73	$1,047.75	$1,047.70