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	$55.27	8.171%	$59.7861	$59.79	$59.80	$59.80
Purchase #2	$131.77	9.296%	$144.0193	$144.02	$144.00	$144.00
Purchase #3	$57.40	8.357%	$62.1969	$62.20	$62.20	$62.20
Purchase #4	$139.92	10.683%	$154.8677	$154.87	$154.85	$154.90
Purchase #5	$62.52	8.158%	$67.6204	$67.62	$67.60	$67.60
Purchase #6	$173.25	7.236%	$185.7864	$185.79	$185.80	$185.80
Purchase #7	$102.60	7.751%	$110.5525	$110.55	$110.55	$110.60
7 purchase totals =	$722.73		$784.8293	$784.84	$784.80	$784.90