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	$117.63	11.519%	$131.1798	$131.18	$131.20	$131.20
Purchase #2	$190.56	9.325%	$208.3297	$208.33	$208.35	$208.30
Purchase #3	$123.50	3.639%	$127.9942	$127.99	$128.00	$128.00
Purchase #4	$12.80	7.457%	$13.7545	$13.75	$13.75	$13.80
Purchase #5	$228.85	11.692%	$255.6071	$255.61	$255.60	$255.60
Purchase #6	$98.52	11.204%	$109.5582	$109.56	$109.55	$109.60
Purchase #7	$84.25	5.498%	$88.8821	$88.88	$88.90	$88.90
7 purchase totals =	$856.11		$935.3056	$935.30	$935.35	$935.40