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	$40.71	4.113%	$42.3844	$42.38	$42.40	$42.40
Purchase #2	$130.71	11.164%	$145.3025	$145.30	$145.30	$145.30
Purchase #3	$219.40	6.653%	$233.9967	$234.00	$234.00	$234.00
Purchase #4	$184.42	11.459%	$205.5527	$205.55	$205.55	$205.60
Purchase #5	$217.77	11.480%	$242.77	$242.77	$242.75	$242.80
Purchase #6	$144.38	12.421%	$162.3134	$162.31	$162.30	$162.30
Purchase #7	$5.49	12.566%	$6.1799	$6.18	$6.20	$6.20
7 purchase totals =	$942.88		$1,038.4996	$1,038.49	$1,038.50	$1,038.60