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	$145.97	13.454%	$165.6088	$165.61	$165.60	$165.60
Purchase #2	$15.76	11.152%	$17.5176	$17.52	$17.50	$17.50
Purchase #3	$237.87	13.207%	$269.2855	$269.29	$269.30	$269.30
Purchase #4	$242.51	11.340%	$270.0106	$270.01	$270.00	$270.00
Purchase #5	$88.49	6.585%	$94.3171	$94.32	$94.30	$94.30
Purchase #6	$71.79	12.307%	$80.6252	$80.63	$80.65	$80.60
Purchase #7	$181.56	4.255%	$189.2854	$189.29	$189.30	$189.30
7 purchase totals =	$983.95		$1,086.6502	$1,086.67	$1,086.65	$1,086.60