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	$18.41	4.736%	$19.2819	$19.28	$19.30	$19.30
Purchase #2	$155.30	6.714%	$165.7268	$165.73	$165.75	$165.70
Purchase #3	$77.41	4.541%	$80.9252	$80.93	$80.95	$80.90
Purchase #4	$151.44	13.419%	$171.7617	$171.76	$171.75	$171.80
Purchase #5	$124.90	10.144%	$137.5699	$137.57	$137.55	$137.60
Purchase #6	$198.46	5.467%	$209.3098	$209.31	$209.30	$209.30
Purchase #7	$211.80	10.374%	$233.7721	$233.77	$233.75	$233.80
7 purchase totals =	$937.72		$1,018.3474	$1,018.35	$1,018.35	$1,018.40