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	$39.33	10.691%	$43.5348	$43.53	$43.55	$43.50
Purchase #2	$155.75	10.255%	$171.7222	$171.72	$171.70	$171.70
Purchase #3	$35.77	13.663%	$40.6573	$40.66	$40.65	$40.70
Purchase #4	$232.92	13.522%	$264.4154	$264.42	$264.40	$264.40
Purchase #5	$81.64	12.589%	$91.9177	$91.92	$91.90	$91.90
Purchase #6	$20.47	11.451%	$22.814	$22.81	$22.80	$22.80
Purchase #7	$140.44	7.224%	$150.5854	$150.59	$150.60	$150.60
7 purchase totals =	$706.32		$785.6468	$785.65	$785.60	$785.60