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	$163.93	5.230%	$172.5035	$172.50	$172.50	$172.50
Purchase #2	$197.28	6.338%	$209.7836	$209.78	$209.80	$209.80
Purchase #3	$128.41	8.692%	$139.5714	$139.57	$139.55	$139.60
Purchase #4	$200.77	12.445%	$225.7558	$225.76	$225.75	$225.80
Purchase #5	$124.77	9.256%	$136.3187	$136.32	$136.30	$136.30
Purchase #6	$178.47	3.819%	$185.2858	$185.29	$185.30	$185.30
Purchase #7	$31.54	4.370%	$32.9183	$32.92	$32.90	$32.90
7 purchase totals =	$1,025.17		$1,102.1371	$1,102.14	$1,102.10	$1,102.20