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	$184.76	13.203%	$209.1539	$209.15	$209.15	$209.20
Purchase #2	$21.88	10.206%	$24.1131	$24.11	$24.10	$24.10
Purchase #3	$72.76	8.345%	$78.8318	$78.83	$78.85	$78.80
Purchase #4	$185.98	6.343%	$197.7767	$197.78	$197.80	$197.80
Purchase #5	$74.83	4.506%	$78.2018	$78.20	$78.20	$78.20
Purchase #6	$32.64	8.702%	$35.4803	$35.48	$35.50	$35.50
Purchase #7	$141.60	7.713%	$152.5216	$152.52	$152.50	$152.50
7 purchase totals =	$714.45		$776.0792	$776.07	$776.10	$776.10