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	$75.29	12.591%	$84.7698	$84.77	$84.75	$84.80
Purchase #2	$135.53	6.477%	$144.3083	$144.31	$144.30	$144.30
Purchase #3	$130.69	8.134%	$141.3203	$141.32	$141.30	$141.30
Purchase #4	$233.62	11.123%	$259.6056	$259.61	$259.60	$259.60
Purchase #5	$199.72	11.256%	$222.2005	$222.20	$222.20	$222.20
Purchase #6	$62.72	10.269%	$69.1607	$69.16	$69.15	$69.20
Purchase #7	$29.76	11.345%	$33.1363	$33.14	$33.15	$33.10
7 purchase totals =	$867.33		$954.5015	$954.51	$954.45	$954.50