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	$7.57	4.294%	$7.8951	$7.90	$7.90	$7.90
Purchase #2	$191.68	3.632%	$198.6418	$198.64	$198.65	$198.60
Purchase #3	$106.32	4.834%	$111.4595	$111.46	$111.45	$111.50
Purchase #4	$192.36	12.290%	$216.001	$216.00	$216.00	$216.00
Purchase #5	$238.56	11.151%	$265.1618	$265.16	$265.15	$265.20
Purchase #6	$127.86	9.302%	$139.7535	$139.75	$139.75	$139.80
Purchase #7	$101.42	9.178%	$110.7283	$110.73	$110.75	$110.70
7 purchase totals =	$965.77		$1,049.6410	$1,049.64	$1,049.65	$1,049.70