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	$25.80	3.176%	$26.6194	$26.62	$26.60	$26.60
Purchase #2	$131.69	7.787%	$141.9447	$141.94	$141.95	$141.90
Purchase #3	$225.53	4.334%	$235.3045	$235.30	$235.30	$235.30
Purchase #4	$191.74	10.328%	$211.5429	$211.54	$211.55	$211.50
Purchase #5	$25.61	12.743%	$28.8735	$28.87	$28.85	$28.90
Purchase #6	$159.87	7.302%	$171.5437	$171.54	$171.55	$171.50
Purchase #7	$242.51	5.298%	$255.3582	$255.36	$255.35	$255.40
7 purchase totals =	$1,002.75		$1,071.1869	$1,071.17	$1,071.15	$1,071.10