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	$73.68	11.534%	$82.1783	$82.18	$82.20	$82.20
Purchase #2	$249.76	11.829%	$279.3041	$279.30	$279.30	$279.30
Purchase #3	$46.31	8.469%	$50.232	$50.23	$50.25	$50.20
Purchase #4	$89.40	8.429%	$96.9355	$96.94	$96.95	$96.90
Purchase #5	$210.89	13.791%	$239.9738	$239.97	$239.95	$240.00
Purchase #6	$82.99	7.543%	$89.2499	$89.25	$89.25	$89.20
Purchase #7	$141.79	10.657%	$156.9006	$156.90	$156.90	$156.90
7 purchase totals =	$894.82		$994.7742	$994.77	$994.80	$994.70