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	$19.49	7.299%	$20.9126	$20.91	$20.90	$20.90
Purchase #2	$246.95	3.310%	$255.124	$255.12	$255.10	$255.10
Purchase #3	$65.41	9.833%	$71.8418	$71.84	$71.85	$71.80
Purchase #4	$104.86	9.104%	$114.4065	$114.41	$114.40	$114.40
Purchase #5	$52.81	9.614%	$57.8872	$57.89	$57.90	$57.90
Purchase #6	$126.99	3.549%	$131.4969	$131.50	$131.50	$131.50
Purchase #7	$64.27	6.747%	$68.6063	$68.61	$68.60	$68.60
7 purchase totals =	$680.78		$720.2753	$720.28	$720.25	$720.20