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	$10.54	9.175%	$11.507	$11.51	$11.50	$11.50
Purchase #2	$51.84	7.696%	$55.8296	$55.83	$55.85	$55.80
Purchase #3	$165.36	12.280%	$185.6662	$185.67	$185.65	$185.70
Purchase #4	$153.32	9.112%	$167.2905	$167.29	$167.30	$167.30
Purchase #5	$89.49	12.667%	$100.8257	$100.83	$100.85	$100.80
Purchase #6	$173.58	11.240%	$193.0904	$193.09	$193.10	$193.10
Purchase #7	$72.28	5.560%	$76.2988	$76.30	$76.30	$76.30
7 purchase totals =	$716.41		$790.5082	$790.52	$790.55	$790.50