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	$250.49	11.753%	$279.9301	$279.93	$279.95	$279.90
Purchase #2	$37.98	4.237%	$39.5892	$39.59	$39.60	$39.60
Purchase #3	$184.48	9.197%	$201.4466	$201.45	$201.45	$201.40
Purchase #4	$105.61	3.315%	$109.111	$109.11	$109.10	$109.10
Purchase #5	$250.77	10.465%	$277.0131	$277.01	$277.00	$277.00
Purchase #6	$78.86	9.144%	$86.071	$86.07	$86.05	$86.10
Purchase #7	$153.26	7.701%	$165.0626	$165.06	$165.05	$165.10
7 purchase totals =	$1,061.45		$1,158.2236	$1,158.22	$1,158.20	$1,158.20