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	$5.34	10.304%	$5.8902	$5.89	$5.90	$5.90
Purchase #2	$29.83	7.738%	$32.1382	$32.14	$32.15	$32.10
Purchase #3	$153.53	9.732%	$168.4715	$168.47	$168.45	$168.50
Purchase #4	$172.82	13.404%	$195.9848	$195.98	$196.00	$196.00
Purchase #5	$99.93	3.317%	$103.2447	$103.24	$103.25	$103.20
Purchase #6	$32.69	6.180%	$34.7102	$34.71	$34.70	$34.70
Purchase #7	$42.98	3.210%	$44.3597	$44.36	$44.35	$44.40
7 purchase totals =	$537.12		$584.7993	$584.79	$584.80	$584.80