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	$30.55	6.182%	$32.4386	$32.44	$32.45	$32.40
Purchase #2	$189.43	7.333%	$203.3209	$203.32	$203.30	$203.30
Purchase #3	$132.36	5.593%	$139.7629	$139.76	$139.75	$139.80
Purchase #4	$144.25	4.621%	$150.9158	$150.92	$150.90	$150.90
Purchase #5	$78.65	5.384%	$82.8845	$82.88	$82.90	$82.90
Purchase #6	$170.88	8.689%	$185.7278	$185.73	$185.75	$185.70
Purchase #7	$180.83	13.778%	$205.7448	$205.74	$205.75	$205.70
7 purchase totals =	$926.95		$1,000.7953	$1,000.79	$1,000.80	$1,000.70