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	$250.44	6.548%	$266.8388	$266.84	$266.85	$266.80
Purchase #2	$196.40	4.546%	$205.3283	$205.33	$205.35	$205.30
Purchase #3	$19.60	6.761%	$20.9252	$20.93	$20.95	$20.90
Purchase #4	$152.27	10.273%	$167.9127	$167.91	$167.90	$167.90
Purchase #5	$25.54	10.820%	$28.3034	$28.30	$28.30	$28.30
Purchase #6	$80.75	3.361%	$83.464	$83.46	$83.45	$83.50
Purchase #7	$91.66	5.732%	$96.914	$96.91	$96.90	$96.90
7 purchase totals =	$816.66		$869.6864	$869.68	$869.70	$869.60