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	$150.30	13.505%	$170.598	$170.60	$170.60	$170.60
Purchase #2	$93.97	13.335%	$106.5009	$106.50	$106.50	$106.50
Purchase #3	$211.71	9.565%	$231.9601	$231.96	$231.95	$232.00
Purchase #4	$100.77	12.683%	$113.5507	$113.55	$113.55	$113.60
Purchase #5	$78.88	8.229%	$85.371	$85.37	$85.35	$85.40
Purchase #6	$131.32	6.324%	$139.6247	$139.62	$139.60	$139.60
Purchase #7	$59.84	8.481%	$64.915	$64.92	$64.90	$64.90
7 purchase totals =	$826.79		$912.5204	$912.52	$912.45	$912.60