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	$28.93	7.389%	$31.0676	$31.07	$31.05	$31.10
Purchase #2	$94.60	9.694%	$103.7705	$103.77	$103.75	$103.80
Purchase #3	$137.71	10.432%	$152.0759	$152.08	$152.10	$152.10
Purchase #4	$160.66	12.350%	$180.5015	$180.50	$180.50	$180.50
Purchase #5	$52.46	8.334%	$56.832	$56.83	$56.85	$56.80
Purchase #6	$139.56	11.168%	$155.1461	$155.15	$155.15	$155.10
Purchase #7	$170.58	5.469%	$179.909	$179.91	$179.90	$179.90
7 purchase totals =	$784.50		$859.3026	$859.31	$859.30	$859.30