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	$74.94	4.774%	$78.5176	$78.52	$78.50	$78.50
Purchase #2	$249.78	9.419%	$273.3068	$273.31	$273.30	$273.30
Purchase #3	$95.37	6.560%	$101.6263	$101.63	$101.65	$101.60
Purchase #4	$58.43	4.716%	$61.1856	$61.19	$61.20	$61.20
Purchase #5	$87.45	13.831%	$99.5452	$99.55	$99.55	$99.50
Purchase #6	$109.46	12.332%	$122.9586	$122.96	$122.95	$123.00
Purchase #7	$23.29	8.367%	$25.2387	$25.24	$25.25	$25.20
7 purchase totals =	$698.72		$762.3788	$762.40	$762.40	$762.30