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	$67.33	6.132%	$71.4587	$71.46	$71.45	$71.50
Purchase #2	$184.52	11.265%	$205.3062	$205.31	$205.30	$205.30
Purchase #3	$113.88	6.690%	$121.4986	$121.50	$121.50	$121.50
Purchase #4	$172.33	6.365%	$183.2988	$183.30	$183.30	$183.30
Purchase #5	$167.93	12.388%	$188.7332	$188.73	$188.75	$188.70
Purchase #6	$113.68	12.446%	$127.8286	$127.83	$127.85	$127.80
Purchase #7	$157.77	13.292%	$178.7408	$178.74	$178.75	$178.70
7 purchase totals =	$977.44		$1,076.8649	$1,076.87	$1,076.90	$1,076.80