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	$166.36	9.274%	$181.7882	$181.79	$181.80	$181.80
Purchase #2	$172.33	7.506%	$185.2651	$185.27	$185.25	$185.30
Purchase #3	$23.76	3.104%	$24.4975	$24.50	$24.50	$24.50
Purchase #4	$26.49	13.618%	$30.0974	$30.10	$30.10	$30.10
Purchase #5	$157.88	4.303%	$164.6736	$164.67	$164.65	$164.70
Purchase #6	$28.82	13.763%	$32.7865	$32.79	$32.80	$32.80
Purchase #7	$114.72	11.415%	$127.8153	$127.82	$127.80	$127.80
7 purchase totals =	$690.36		$746.9236	$746.94	$746.90	$747.00