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	$119.99	8.244%	$129.882	$129.88	$129.90	$129.90
Purchase #2	$190.60	13.270%	$215.8926	$215.89	$215.90	$215.90
Purchase #3	$209.71	5.634%	$221.5251	$221.53	$221.55	$221.50
Purchase #4	$173.56	8.481%	$188.2796	$188.28	$188.30	$188.30
Purchase #5	$210.34	4.261%	$219.3026	$219.30	$219.30	$219.30
Purchase #6	$127.54	11.663%	$142.415	$142.42	$142.40	$142.40
Purchase #7	$158.72	8.427%	$172.0953	$172.10	$172.10	$172.10
7 purchase totals =	$1,190.46		$1,289.3922	$1,289.40	$1,289.45	$1,289.40