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	$40.89	6.834%	$43.6844	$43.68	$43.70	$43.70
Purchase #2	$76.31	3.671%	$79.1113	$79.11	$79.10	$79.10
Purchase #3	$123.67	6.251%	$131.4006	$131.40	$131.40	$131.40
Purchase #4	$182.78	5.137%	$192.1694	$192.17	$192.15	$192.20
Purchase #5	$17.64	13.541%	$20.0286	$20.03	$20.05	$20.00
Purchase #6	$126.33	13.621%	$143.5374	$143.54	$143.55	$143.50
Purchase #7	$181.59	8.380%	$196.8072	$196.81	$196.80	$196.80
7 purchase totals =	$749.21		$806.7389	$806.74	$806.75	$806.70