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	$148.47	3.623%	$153.8491	$153.85	$153.85	$153.80
Purchase #2	$108.25	6.195%	$114.9561	$114.96	$114.95	$115.00
Purchase #3	$224.33	6.145%	$238.1151	$238.12	$238.10	$238.10
Purchase #4	$39.37	3.783%	$40.8594	$40.86	$40.85	$40.90
Purchase #5	$116.98	3.352%	$120.9012	$120.90	$120.90	$120.90
Purchase #6	$142.67	5.603%	$150.6638	$150.66	$150.65	$150.70
Purchase #7	$147.68	7.506%	$158.7649	$158.76	$158.75	$158.80
7 purchase totals =	$927.75		$978.1096	$978.11	$978.05	$978.20