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	$17.61	9.592%	$19.2992	$19.30	$19.30	$19.30
Purchase #2	$144.76	13.381%	$164.1303	$164.13	$164.15	$164.10
Purchase #3	$82.89	11.842%	$92.7058	$92.71	$92.70	$92.70
Purchase #4	$65.57	10.853%	$72.6863	$72.69	$72.70	$72.70
Purchase #5	$171.72	5.528%	$181.2127	$181.21	$181.20	$181.20
Purchase #6	$210.74	6.353%	$224.1283	$224.13	$224.15	$224.10
Purchase #7	$106.56	13.373%	$120.8103	$120.81	$120.80	$120.80
7 purchase totals =	$799.85		$874.9729	$874.98	$875.00	$874.90