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	$137.36	4.291%	$143.2541	$143.25	$143.25	$143.30
Purchase #2	$160.37	7.465%	$172.3416	$172.34	$172.35	$172.30
Purchase #3	$250.83	6.191%	$266.3589	$266.36	$266.35	$266.40
Purchase #4	$245.53	3.458%	$254.0204	$254.02	$254.00	$254.00
Purchase #5	$19.76	8.320%	$21.404	$21.40	$21.40	$21.40
Purchase #6	$120.46	9.241%	$131.5917	$131.59	$131.60	$131.60
Purchase #7	$137.74	5.510%	$145.3295	$145.33	$145.35	$145.30
7 purchase totals =	$1,072.05		$1,134.3002	$1,134.29	$1,134.30	$1,134.30