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	$39.59	9.290%	$43.2679	$43.27	$43.25	$43.30
Purchase #2	$105.28	12.354%	$118.2863	$118.29	$118.30	$118.30
Purchase #3	$185.56	13.707%	$210.9947	$210.99	$211.00	$211.00
Purchase #4	$218.37	3.121%	$225.1853	$225.19	$225.20	$225.20
Purchase #5	$112.90	6.830%	$120.6111	$120.61	$120.60	$120.60
Purchase #6	$152.65	11.259%	$169.8369	$169.84	$169.85	$169.80
Purchase #7	$78.28	5.554%	$82.6277	$82.63	$82.65	$82.60
7 purchase totals =	$892.63		$970.8099	$970.82	$970.85	$970.80