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	$243.51	8.826%	$265.0022	$265.00	$265.00	$265.00
Purchase #2	$99.27	12.600%	$111.778	$111.78	$111.80	$111.80
Purchase #3	$139.40	10.266%	$153.7108	$153.71	$153.70	$153.70
Purchase #4	$114.38	5.446%	$120.6091	$120.61	$120.60	$120.60
Purchase #5	$41.36	10.317%	$45.6271	$45.63	$45.65	$45.60
Purchase #6	$237.60	7.300%	$254.9448	$254.94	$254.95	$254.90
Purchase #7	$91.40	7.514%	$98.2678	$98.27	$98.25	$98.30
7 purchase totals =	$966.92		$1,049.9398	$1,049.94	$1,049.95	$1,049.90