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	$31.32	13.248%	$35.4693	$35.47	$35.45	$35.50
Purchase #2	$72.60	9.343%	$79.383	$79.38	$79.40	$79.40
Purchase #3	$127.54	9.345%	$139.4586	$139.46	$139.45	$139.50
Purchase #4	$185.67	10.547%	$205.2526	$205.25	$205.25	$205.30
Purchase #5	$42.50	6.287%	$45.172	$45.17	$45.15	$45.20
Purchase #6	$240.52	10.396%	$265.5245	$265.52	$265.50	$265.50
Purchase #7	$150.97	12.590%	$169.9771	$169.98	$170.00	$170.00
7 purchase totals =	$851.12		$940.2371	$940.23	$940.20	$940.40