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	$237.58	3.167%	$245.1042	$245.10	$245.10	$245.10
Purchase #2	$66.46	8.788%	$72.3005	$72.30	$72.30	$72.30
Purchase #3	$110.75	13.300%	$125.4798	$125.48	$125.50	$125.50
Purchase #4	$209.71	9.592%	$229.8254	$229.83	$229.85	$229.80
Purchase #5	$108.39	3.180%	$111.8368	$111.84	$111.85	$111.80
Purchase #6	$83.54	4.235%	$87.0779	$87.08	$87.10	$87.10
Purchase #7	$31.92	6.356%	$33.9488	$33.95	$33.95	$33.90
7 purchase totals =	$848.35		$905.5734	$905.58	$905.65	$905.50