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	$239.32	11.512%	$266.8705	$266.87	$266.85	$266.90
Purchase #2	$53.28	7.745%	$57.4065	$57.41	$57.40	$57.40
Purchase #3	$129.65	7.196%	$138.9796	$138.98	$139.00	$139.00
Purchase #4	$74.28	3.533%	$76.9043	$76.90	$76.90	$76.90
Purchase #5	$128.71	6.663%	$137.2859	$137.29	$137.30	$137.30
Purchase #6	$173.57	5.151%	$182.5106	$182.51	$182.50	$182.50
Purchase #7	$124.67	13.523%	$141.5291	$141.53	$141.55	$141.50
7 purchase totals =	$923.48		$1,001.4865	$1,001.49	$1,001.50	$1,001.50