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	$179.52	3.778%	$186.3023	$186.30	$186.30	$186.30
Purchase #2	$85.31	3.567%	$88.353	$88.35	$88.35	$88.40
Purchase #3	$131.85	12.329%	$148.1058	$148.11	$148.10	$148.10
Purchase #4	$245.40	8.563%	$266.4136	$266.41	$266.40	$266.40
Purchase #5	$28.55	10.484%	$31.5432	$31.54	$31.55	$31.50
Purchase #6	$122.40	5.310%	$128.8994	$128.90	$128.90	$128.90
Purchase #7	$46.54	9.790%	$51.0963	$51.10	$51.10	$51.10
7 purchase totals =	$839.57		$900.7136	$900.71	$900.70	$900.70