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	$206.36	8.824%	$224.5692	$224.57	$224.55	$224.60
Purchase #2	$153.91	10.143%	$169.5211	$169.52	$169.50	$169.50
Purchase #3	$85.40	4.507%	$89.249	$89.25	$89.25	$89.20
Purchase #4	$122.45	13.823%	$139.3763	$139.38	$139.40	$139.40
Purchase #5	$144.50	3.741%	$149.9057	$149.91	$149.90	$149.90
Purchase #6	$20.28	12.805%	$22.8769	$22.88	$22.90	$22.90
Purchase #7	$167.32	6.592%	$178.3497	$178.35	$178.35	$178.30
7 purchase totals =	$900.22		$973.8479	$973.86	$973.85	$973.80