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	$226.48	6.185%	$240.4878	$240.49	$240.50	$240.50
Purchase #2	$157.39	4.752%	$164.8692	$164.87	$164.85	$164.90
Purchase #3	$169.92	9.355%	$185.816	$185.82	$185.80	$185.80
Purchase #4	$53.97	10.596%	$59.6887	$59.69	$59.70	$59.70
Purchase #5	$234.98	10.355%	$259.3122	$259.31	$259.30	$259.30
Purchase #6	$99.47	7.587%	$107.0168	$107.02	$107.00	$107.00
Purchase #7	$172.93	13.257%	$195.8553	$195.86	$195.85	$195.90
7 purchase totals =	$1,115.14		$1,213.0460	$1,213.06	$1,213.00	$1,213.10