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	$68.31	9.415%	$74.7414	$74.74	$74.75	$74.70
Purchase #2	$37.61	7.162%	$40.3036	$40.30	$40.30	$40.30
Purchase #3	$137.90	11.219%	$153.371	$153.37	$153.35	$153.40
Purchase #4	$161.79	11.169%	$179.8603	$179.86	$179.85	$179.90
Purchase #5	$81.34	4.802%	$85.2459	$85.25	$85.25	$85.20
Purchase #6	$243.96	10.720%	$270.1125	$270.11	$270.10	$270.10
Purchase #7	$169.59	4.143%	$176.6161	$176.62	$176.60	$176.60
7 purchase totals =	$900.50		$980.2508	$980.25	$980.20	$980.20