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	$37.66	10.736%	$41.7032	$41.70	$41.70	$41.70
Purchase #2	$209.68	6.856%	$224.0557	$224.06	$224.05	$224.10
Purchase #3	$219.61	9.333%	$240.1062	$240.11	$240.10	$240.10
Purchase #4	$38.71	7.361%	$41.5594	$41.56	$41.55	$41.60
Purchase #5	$126.74	4.765%	$132.7792	$132.78	$132.80	$132.80
Purchase #6	$225.51	13.226%	$255.336	$255.34	$255.35	$255.30
Purchase #7	$180.98	5.800%	$191.4768	$191.48	$191.50	$191.50
7 purchase totals =	$1,038.89		$1,127.0165	$1,127.03	$1,127.05	$1,127.10