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	$8.97	10.489%	$9.9109	$9.91	$9.90	$9.90
Purchase #2	$79.83	3.754%	$82.8268	$82.83	$82.85	$82.80
Purchase #3	$161.93	6.822%	$172.9769	$172.98	$173.00	$173.00
Purchase #4	$96.67	13.802%	$110.0124	$110.01	$110.00	$110.00
Purchase #5	$89.96	10.207%	$99.1422	$99.14	$99.15	$99.10
Purchase #6	$124.36	5.735%	$131.492	$131.49	$131.50	$131.50
Purchase #7	$103.73	4.539%	$108.4383	$108.44	$108.45	$108.40
7 purchase totals =	$665.45		$714.7995	$714.80	$714.85	$714.70