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	$93.43	10.784%	$103.5055	$103.51	$103.50	$103.50
Purchase #2	$111.71	5.341%	$117.6764	$117.68	$117.70	$117.70
Purchase #3	$29.70	12.340%	$33.365	$33.37	$33.35	$33.40
Purchase #4	$156.31	3.482%	$161.7527	$161.75	$161.75	$161.80
Purchase #5	$31.40	8.455%	$34.0549	$34.05	$34.05	$34.10
Purchase #6	$182.53	4.705%	$191.118	$191.12	$191.10	$191.10
Purchase #7	$154.96	11.292%	$172.4581	$172.46	$172.45	$172.50
7 purchase totals =	$760.04		$813.9306	$813.94	$813.90	$814.10