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	$241.44	6.345%	$256.7594	$256.76	$256.75	$256.80
Purchase #2	$40.79	11.428%	$45.4515	$45.45	$45.45	$45.50
Purchase #3	$106.56	9.220%	$116.3848	$116.38	$116.40	$116.40
Purchase #4	$217.49	5.648%	$229.7738	$229.77	$229.75	$229.80
Purchase #5	$97.90	12.337%	$109.9779	$109.98	$110.00	$110.00
Purchase #6	$44.59	9.254%	$48.7164	$48.72	$48.70	$48.70
Purchase #7	$61.41	6.345%	$65.3065	$65.31	$65.30	$65.30
7 purchase totals =	$810.18		$872.3703	$872.37	$872.35	$872.50