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	$131.45	6.114%	$139.4869	$139.49	$139.50	$139.50
Purchase #2	$121.37	12.715%	$136.8022	$136.80	$136.80	$136.80
Purchase #3	$93.53	4.578%	$97.8118	$97.81	$97.80	$97.80
Purchase #4	$80.33	11.254%	$89.3703	$89.37	$89.35	$89.40
Purchase #5	$159.71	3.123%	$164.6977	$164.70	$164.70	$164.70
Purchase #6	$79.31	12.431%	$89.169	$89.17	$89.15	$89.20
Purchase #7	$164.80	7.459%	$177.0924	$177.09	$177.10	$177.10
7 purchase totals =	$830.50		$894.4303	$894.43	$894.40	$894.50