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	$217.86	11.385%	$242.6634	$242.66	$242.65	$242.70
Purchase #2	$101.43	11.147%	$112.7364	$112.74	$112.75	$112.70
Purchase #3	$123.40	11.682%	$137.8156	$137.82	$137.80	$137.80
Purchase #4	$78.81	13.632%	$89.5534	$89.55	$89.55	$89.60
Purchase #5	$71.95	8.547%	$78.0996	$78.10	$78.10	$78.10
Purchase #6	$82.92	6.255%	$88.1066	$88.11	$88.10	$88.10
Purchase #7	$129.93	9.615%	$142.4228	$142.42	$142.40	$142.40
7 purchase totals =	$806.30		$891.3978	$891.40	$891.35	$891.40