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	$131.32	8.198%	$142.0856	$142.09	$142.10	$142.10
Purchase #2	$171.59	6.481%	$182.7107	$182.71	$182.70	$182.70
Purchase #3	$52.32	4.744%	$54.8021	$54.80	$54.80	$54.80
Purchase #4	$129.52	7.759%	$139.5695	$139.57	$139.55	$139.60
Purchase #5	$77.38	8.332%	$83.8273	$83.83	$83.85	$83.80
Purchase #6	$88.61	13.526%	$100.5954	$100.60	$100.60	$100.60
Purchase #7	$125.41	13.168%	$141.924	$141.92	$141.90	$141.90
7 purchase totals =	$776.15		$845.5146	$845.52	$845.50	$845.50