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	$135.56	10.703%	$150.069	$150.07	$150.05	$150.10
Purchase #2	$148.72	4.139%	$154.8755	$154.88	$154.90	$154.90
Purchase #3	$41.35	11.618%	$46.154	$46.15	$46.15	$46.20
Purchase #4	$124.71	7.484%	$134.0433	$134.04	$134.05	$134.00
Purchase #5	$89.72	3.550%	$92.9051	$92.91	$92.90	$92.90
Purchase #6	$173.88	13.141%	$196.7296	$196.73	$196.75	$196.70
Purchase #7	$80.70	13.576%	$91.6558	$91.66	$91.65	$91.70
7 purchase totals =	$794.64		$866.4323	$866.44	$866.45	$866.50