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	$65.39	7.538%	$70.3191	$70.32	$70.30	$70.30
Purchase #2	$182.91	4.344%	$190.8556	$190.86	$190.85	$190.90
Purchase #3	$10.85	10.375%	$11.9757	$11.98	$12.00	$12.00
Purchase #4	$170.75	9.230%	$186.5102	$186.51	$186.50	$186.50
Purchase #5	$135.29	6.474%	$144.0487	$144.05	$144.05	$144.00
Purchase #6	$213.27	5.157%	$224.2683	$224.27	$224.25	$224.30
Purchase #7	$233.30	8.492%	$253.1118	$253.11	$253.10	$253.10
7 purchase totals =	$1,011.76		$1,081.0894	$1,081.10	$1,081.05	$1,081.10