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	$152.78	11.623%	$170.5376	$170.54	$170.55	$170.50
Purchase #2	$58.46	6.541%	$62.2839	$62.28	$62.30	$62.30
Purchase #3	$244.71	8.263%	$264.9304	$264.93	$264.95	$264.90
Purchase #4	$46.91	13.736%	$53.3536	$53.35	$53.35	$53.40
Purchase #5	$168.80	5.453%	$178.0047	$178.00	$178.00	$178.00
Purchase #6	$229.74	11.387%	$255.9005	$255.90	$255.90	$255.90
Purchase #7	$137.25	10.184%	$151.2275	$151.23	$151.25	$151.20
7 purchase totals =	$1,038.65		$1,136.2382	$1,136.23	$1,136.30	$1,136.20