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	$36.42	7.569%	$39.1766	$39.18	$39.20	$39.20
Purchase #2	$94.37	4.594%	$98.7054	$98.71	$98.70	$98.70
Purchase #3	$245.50	11.743%	$274.3291	$274.33	$274.35	$274.30
Purchase #4	$142.88	11.340%	$159.0826	$159.08	$159.10	$159.10
Purchase #5	$153.83	7.552%	$165.4472	$165.45	$165.45	$165.40
Purchase #6	$105.31	5.465%	$111.0652	$111.07	$111.05	$111.10
Purchase #7	$103.70	9.200%	$113.2404	$113.24	$113.25	$113.20
7 purchase totals =	$882.01		$961.0465	$961.06	$961.10	$961.00