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	$123.77	6.208%	$131.4536	$131.45	$131.45	$131.50
Purchase #2	$44.74	7.795%	$48.2275	$48.23	$48.25	$48.20
Purchase #3	$129.85	8.589%	$141.0028	$141.00	$141.00	$141.00
Purchase #4	$224.31	7.394%	$240.8955	$240.90	$240.90	$240.90
Purchase #5	$39.42	4.373%	$41.1438	$41.14	$41.15	$41.10
Purchase #6	$68.27	6.644%	$72.8059	$72.81	$72.80	$72.80
Purchase #7	$188.64	11.297%	$209.9507	$209.95	$209.95	$210.00
7 purchase totals =	$819.00		$885.4798	$885.48	$885.50	$885.50