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	$98.41	11.220%	$109.4516	$109.45	$109.45	$109.50
Purchase #2	$170.27	10.302%	$187.8112	$187.81	$187.80	$187.80
Purchase #3	$196.73	12.121%	$220.5756	$220.58	$220.60	$220.60
Purchase #4	$196.40	4.802%	$205.8311	$205.83	$205.85	$205.80
Purchase #5	$129.49	12.111%	$145.1725	$145.17	$145.15	$145.20
Purchase #6	$55.76	12.245%	$62.5878	$62.59	$62.60	$62.60
Purchase #7	$227.26	12.586%	$255.8629	$255.86	$255.85	$255.90
7 purchase totals =	$1,074.32		$1,187.2927	$1,187.29	$1,187.30	$1,187.40