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	$28.48	10.262%	$31.4026	$31.40	$31.40	$31.40
Purchase #2	$89.73	5.783%	$94.9191	$94.92	$94.90	$94.90
Purchase #3	$34.50	5.601%	$36.4323	$36.43	$36.45	$36.40
Purchase #4	$105.34	13.581%	$119.6462	$119.65	$119.65	$119.60
Purchase #5	$5.64	13.470%	$6.3997	$6.40	$6.40	$6.40
Purchase #6	$21.43	4.424%	$22.3781	$22.38	$22.40	$22.40
Purchase #7	$173.54	9.422%	$189.8909	$189.89	$189.90	$189.90
7 purchase totals =	$458.66		$501.0689	$501.07	$501.10	$501.00