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	$47.61	13.481%	$54.0283	$54.03	$54.05	$54.00
Purchase #2	$149.62	12.131%	$167.7704	$167.77	$167.75	$167.80
Purchase #3	$94.53	9.113%	$103.1445	$103.14	$103.15	$103.10
Purchase #4	$41.91	11.625%	$46.782	$46.78	$46.80	$46.80
Purchase #5	$44.88	4.235%	$46.7807	$46.78	$46.80	$46.80
Purchase #6	$240.98	5.329%	$253.8218	$253.82	$253.80	$253.80
Purchase #7	$11.32	12.494%	$12.7343	$12.73	$12.75	$12.70
7 purchase totals =	$630.85		$685.0620	$685.05	$685.10	$685.00