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	$82.92	10.179%	$91.3604	$91.36	$91.35	$91.40
Purchase #2	$81.64	13.347%	$92.5365	$92.54	$92.55	$92.50
Purchase #3	$82.98	8.693%	$90.1935	$90.19	$90.20	$90.20
Purchase #4	$74.89	8.449%	$81.2175	$81.22	$81.20	$81.20
Purchase #5	$91.43	4.837%	$95.8525	$95.85	$95.85	$95.90
Purchase #6	$144.83	7.858%	$156.2107	$156.21	$156.20	$156.20
Purchase #7	$34.63	11.167%	$38.4971	$38.50	$38.50	$38.50
7 purchase totals =	$593.32		$645.8682	$645.87	$645.85	$645.90