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	$106.68	9.542%	$116.8594	$116.86	$116.85	$116.90
Purchase #2	$63.35	3.118%	$65.3253	$65.33	$65.35	$65.30
Purchase #3	$222.37	10.552%	$245.8345	$245.83	$245.85	$245.80
Purchase #4	$92.85	7.617%	$99.9224	$99.92	$99.90	$99.90
Purchase #5	$79.50	12.530%	$89.4614	$89.46	$89.45	$89.50
Purchase #6	$204.98	12.376%	$230.3483	$230.35	$230.35	$230.30
Purchase #7	$242.99	12.774%	$274.0295	$274.03	$274.05	$274.00
7 purchase totals =	$1,012.72		$1,121.7808	$1,121.78	$1,121.80	$1,121.70