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	$167.56	10.635%	$185.38	$185.38	$185.40	$185.40
Purchase #2	$204.76	4.326%	$213.6179	$213.62	$213.60	$213.60
Purchase #3	$101.39	6.281%	$107.7583	$107.76	$107.75	$107.80
Purchase #4	$82.94	7.609%	$89.2509	$89.25	$89.25	$89.30
Purchase #5	$42.46	11.406%	$47.303	$47.30	$47.30	$47.30
Purchase #6	$229.25	13.296%	$259.7311	$259.73	$259.75	$259.70
Purchase #7	$87.92	12.343%	$98.772	$98.77	$98.75	$98.80
7 purchase totals =	$916.28		$1,001.8132	$1,001.81	$1,001.80	$1,001.90