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	$111.71	13.199%	$126.4546	$126.45	$126.45	$126.50
Purchase #2	$81.59	6.433%	$86.8387	$86.84	$86.85	$86.80
Purchase #3	$247.51	10.668%	$273.9144	$273.91	$273.90	$273.90
Purchase #4	$248.93	7.644%	$267.9582	$267.96	$267.95	$268.00
Purchase #5	$11.66	10.717%	$12.9096	$12.91	$12.90	$12.90
Purchase #6	$39.52	10.162%	$43.536	$43.54	$43.55	$43.50
Purchase #7	$155.59	12.291%	$174.7136	$174.71	$174.70	$174.70
7 purchase totals =	$896.51		$986.3251	$986.32	$986.30	$986.30