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	$131.71	11.245%	$146.5208	$146.52	$146.50	$146.50
Purchase #2	$135.30	13.456%	$153.506	$153.51	$153.50	$153.50
Purchase #3	$135.94	11.222%	$151.1952	$151.20	$151.20	$151.20
Purchase #4	$165.55	8.689%	$179.9346	$179.93	$179.95	$179.90
Purchase #5	$175.57	11.531%	$195.815	$195.82	$195.80	$195.80
Purchase #6	$70.67	13.843%	$80.4528	$80.45	$80.45	$80.50
Purchase #7	$89.99	9.341%	$98.396	$98.40	$98.40	$98.40
7 purchase totals =	$904.73		$1,005.8204	$1,005.83	$1,005.80	$1,005.80