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	$202.49	5.774%	$214.1818	$214.18	$214.20	$214.20
Purchase #2	$133.90	12.581%	$150.746	$150.75	$150.75	$150.70
Purchase #3	$211.45	6.801%	$225.8307	$225.83	$225.85	$225.80
Purchase #4	$118.82	4.235%	$123.852	$123.85	$123.85	$123.90
Purchase #5	$18.93	13.563%	$21.4975	$21.50	$21.50	$21.50
Purchase #6	$170.59	12.412%	$191.7636	$191.76	$191.75	$191.80
Purchase #7	$39.61	3.788%	$41.1104	$41.11	$41.10	$41.10
7 purchase totals =	$895.79		$968.9820	$968.98	$969.00	$969.00