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	$28.71	9.793%	$31.5216	$31.52	$31.50	$31.50
Purchase #2	$74.90	10.581%	$82.8252	$82.83	$82.85	$82.80
Purchase #3	$79.74	13.513%	$90.5153	$90.52	$90.50	$90.50
Purchase #4	$75.91	7.560%	$81.6488	$81.65	$81.65	$81.60
Purchase #5	$157.35	10.765%	$174.2887	$174.29	$174.30	$174.30
Purchase #6	$91.60	11.224%	$101.8812	$101.88	$101.90	$101.90
Purchase #7	$114.53	13.566%	$130.0671	$130.07	$130.05	$130.10
7 purchase totals =	$622.74		$692.7479	$692.76	$692.75	$692.70