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	$173.88	3.210%	$179.4615	$179.46	$179.45	$179.50
Purchase #2	$224.26	13.488%	$254.5082	$254.51	$254.50	$254.50
Purchase #3	$169.52	13.790%	$192.8968	$192.90	$192.90	$192.90
Purchase #4	$75.69	12.710%	$85.3102	$85.31	$85.30	$85.30
Purchase #5	$119.68	7.191%	$128.2862	$128.29	$128.30	$128.30
Purchase #6	$19.66	6.678%	$20.9729	$20.97	$20.95	$21.00
Purchase #7	$139.37	6.290%	$148.1364	$148.14	$148.15	$148.10
7 purchase totals =	$922.06		$1,009.5722	$1,009.58	$1,009.55	$1,009.60