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	$245.69	8.632%	$266.898	$266.90	$266.90	$266.90
Purchase #2	$230.61	4.415%	$240.7914	$240.79	$240.80	$240.80
Purchase #3	$91.66	8.156%	$99.1358	$99.14	$99.15	$99.10
Purchase #4	$124.97	13.747%	$142.1496	$142.15	$142.15	$142.10
Purchase #5	$78.28	8.240%	$84.7303	$84.73	$84.75	$84.70
Purchase #6	$144.83	7.367%	$155.4996	$155.50	$155.50	$155.50
Purchase #7	$21.47	12.307%	$24.1123	$24.11	$24.10	$24.10
7 purchase totals =	$937.51		$1,013.3170	$1,013.32	$1,013.35	$1,013.20