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	$211.98	8.200%	$229.3624	$229.36	$229.35	$229.40
Purchase #2	$178.31	4.245%	$185.8793	$185.88	$185.90	$185.90
Purchase #3	$123.51	9.620%	$135.3917	$135.39	$135.40	$135.40
Purchase #4	$229.72	9.257%	$250.9852	$250.99	$251.00	$251.00
Purchase #5	$103.80	3.139%	$107.0583	$107.06	$107.05	$107.10
Purchase #6	$110.86	8.143%	$119.8873	$119.89	$119.90	$119.90
Purchase #7	$79.65	13.358%	$90.2896	$90.29	$90.30	$90.30
7 purchase totals =	$1,037.83		$1,118.8538	$1,118.86	$1,118.90	$1,119.00