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	$34.31	6.116%	$36.4084	$36.41	$36.40	$36.40
Purchase #2	$84.47	6.365%	$89.8465	$89.85	$89.85	$89.80
Purchase #3	$80.76	5.430%	$85.1453	$85.15	$85.15	$85.10
Purchase #4	$50.29	7.572%	$54.098	$54.10	$54.10	$54.10
Purchase #5	$67.31	13.275%	$76.2454	$76.25	$76.25	$76.20
Purchase #6	$141.44	3.685%	$146.6521	$146.65	$146.65	$146.70
Purchase #7	$28.72	13.391%	$32.5659	$32.57	$32.55	$32.60
7 purchase totals =	$487.30		$520.9616	$520.98	$520.95	$520.90