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	$54.98	7.382%	$59.0386	$59.04	$59.05	$59.00
Purchase #2	$40.83	4.583%	$42.7012	$42.70	$42.70	$42.70
Purchase #3	$111.62	12.686%	$125.7801	$125.78	$125.80	$125.80
Purchase #4	$101.88	4.824%	$106.7947	$106.79	$106.80	$106.80
Purchase #5	$138.67	10.764%	$153.5964	$153.60	$153.60	$153.60
Purchase #6	$31.99	4.206%	$33.3355	$33.34	$33.35	$33.30
Purchase #7	$48.73	12.617%	$54.8783	$54.88	$54.90	$54.90
7 purchase totals =	$528.70		$576.1248	$576.13	$576.20	$576.10