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	$86.33	6.236%	$91.7135	$91.71	$91.70	$91.70
Purchase #2	$33.37	12.654%	$37.5926	$37.59	$37.60	$37.60
Purchase #3	$27.76	13.547%	$31.5206	$31.52	$31.50	$31.50
Purchase #4	$92.37	9.499%	$101.1442	$101.14	$101.15	$101.10
Purchase #5	$59.99	3.337%	$61.9919	$61.99	$62.00	$62.00
Purchase #6	$26.64	7.688%	$28.6881	$28.69	$28.70	$28.70
Purchase #7	$147.83	5.868%	$156.5047	$156.50	$156.50	$156.50
7 purchase totals =	$474.29		$509.1556	$509.14	$509.15	$509.10