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	$127.45	7.132%	$136.5397	$136.54	$136.55	$136.50
Purchase #2	$191.44	4.533%	$200.118	$200.12	$200.10	$200.10
Purchase #3	$234.45	10.353%	$258.7226	$258.72	$258.70	$258.70
Purchase #4	$32.52	9.584%	$35.6367	$35.64	$35.65	$35.60
Purchase #5	$100.40	9.213%	$109.6499	$109.65	$109.65	$109.60
Purchase #6	$91.76	5.835%	$97.1142	$97.11	$97.10	$97.10
Purchase #7	$153.60	5.218%	$161.6148	$161.61	$161.60	$161.60
7 purchase totals =	$931.62		$999.3959	$999.39	$999.35	$999.20