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	$174.65	6.270%	$185.6006	$185.60	$185.60	$185.60
Purchase #2	$91.97	9.296%	$100.5195	$100.52	$100.50	$100.50
Purchase #3	$70.25	13.638%	$79.8307	$79.83	$79.85	$79.80
Purchase #4	$234.64	4.150%	$244.3776	$244.38	$244.40	$244.40
Purchase #5	$114.34	4.558%	$119.5516	$119.55	$119.55	$119.60
Purchase #6	$232.56	6.605%	$247.9206	$247.92	$247.90	$247.90
Purchase #7	$172.31	12.549%	$193.9332	$193.93	$193.95	$193.90
7 purchase totals =	$1,090.72		$1,171.7338	$1,171.73	$1,171.75	$1,171.70