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	$80.45	11.725%	$89.8828	$89.88	$89.90	$89.90
Purchase #2	$62.47	8.470%	$67.7612	$67.76	$67.75	$67.80
Purchase #3	$187.92	7.819%	$202.6135	$202.61	$202.60	$202.60
Purchase #4	$120.29	4.551%	$125.7644	$125.76	$125.75	$125.80
Purchase #5	$46.37	8.585%	$50.3509	$50.35	$50.35	$50.40
Purchase #6	$72.96	12.355%	$81.9742	$81.97	$81.95	$82.00
Purchase #7	$200.42	11.526%	$223.5204	$223.52	$223.50	$223.50
7 purchase totals =	$770.88		$841.8674	$841.85	$841.80	$842.00