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	$81.28	11.310%	$90.4728	$90.47	$90.45	$90.50
Purchase #2	$62.96	13.561%	$71.498	$71.50	$71.50	$71.50
Purchase #3	$163.50	8.627%	$177.6051	$177.61	$177.60	$177.60
Purchase #4	$165.29	11.519%	$184.3298	$184.33	$184.35	$184.30
Purchase #5	$9.63	11.223%	$10.7108	$10.71	$10.70	$10.70
Purchase #6	$89.51	12.326%	$100.543	$100.54	$100.55	$100.50
Purchase #7	$203.63	11.340%	$226.7216	$226.72	$226.70	$226.70
7 purchase totals =	$775.80		$861.8811	$861.88	$861.85	$861.80