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	$247.44	7.588%	$266.2157	$266.22	$266.20	$266.20
Purchase #2	$78.45	4.728%	$82.1591	$82.16	$82.15	$82.20
Purchase #3	$129.26	9.435%	$141.4557	$141.46	$141.45	$141.50
Purchase #4	$132.53	6.820%	$141.5685	$141.57	$141.55	$141.60
Purchase #5	$115.67	11.312%	$128.7546	$128.75	$128.75	$128.80
Purchase #6	$62.41	8.510%	$67.7211	$67.72	$67.70	$67.70
Purchase #7	$157.56	4.285%	$164.3114	$164.31	$164.30	$164.30
7 purchase totals =	$923.32		$992.1861	$992.19	$992.10	$992.30