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	$85.53	4.638%	$89.4969	$89.50	$89.50	$89.50
Purchase #2	$210.44	10.787%	$233.1402	$233.14	$233.15	$233.10
Purchase #3	$229.30	10.667%	$253.7594	$253.76	$253.75	$253.80
Purchase #4	$40.36	4.158%	$42.0382	$42.04	$42.05	$42.00
Purchase #5	$222.99	4.862%	$233.8318	$233.83	$233.85	$233.80
Purchase #6	$102.99	6.480%	$109.6638	$109.66	$109.65	$109.70
Purchase #7	$18.36	6.736%	$19.5967	$19.60	$19.60	$19.60
7 purchase totals =	$909.97		$981.5270	$981.53	$981.55	$981.50