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	$88.99	12.619%	$100.2196	$100.22	$100.20	$100.20
Purchase #2	$214.60	6.144%	$227.785	$227.79	$227.80	$227.80
Purchase #3	$87.94	13.780%	$100.0581	$100.06	$100.05	$100.10
Purchase #4	$230.66	10.450%	$254.764	$254.76	$254.75	$254.80
Purchase #5	$102.59	7.136%	$109.9108	$109.91	$109.90	$109.90
Purchase #6	$204.47	13.270%	$231.6032	$231.60	$231.60	$231.60
Purchase #7	$181.55	9.273%	$198.3851	$198.39	$198.40	$198.40
7 purchase totals =	$1,110.80		$1,222.7258	$1,222.73	$1,222.70	$1,222.80