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	$185.75	11.167%	$206.4927	$206.49	$206.50	$206.50
Purchase #2	$132.28	12.473%	$148.7793	$148.78	$148.80	$148.80
Purchase #3	$230.85	8.304%	$250.0198	$250.02	$250.00	$250.00
Purchase #4	$17.32	13.858%	$19.7202	$19.72	$19.70	$19.70
Purchase #5	$71.53	6.535%	$76.2045	$76.20	$76.20	$76.20
Purchase #6	$155.55	8.222%	$168.3393	$168.34	$168.35	$168.30
Purchase #7	$107.82	3.631%	$111.7349	$111.73	$111.75	$111.70
7 purchase totals =	$901.10		$981.2907	$981.28	$981.30	$981.20