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	$86.42	4.685%	$90.4688	$90.47	$90.45	$90.50
Purchase #2	$206.72	10.708%	$228.8556	$228.86	$228.85	$228.90
Purchase #3	$222.40	3.318%	$229.7792	$229.78	$229.80	$229.80
Purchase #4	$162.58	8.863%	$176.9895	$176.99	$177.00	$177.00
Purchase #5	$152.43	6.223%	$161.9157	$161.92	$161.90	$161.90
Purchase #6	$80.50	8.428%	$87.2845	$87.28	$87.30	$87.30
Purchase #7	$206.67	4.780%	$216.5488	$216.55	$216.55	$216.50
7 purchase totals =	$1,117.72		$1,191.8421	$1,191.85	$1,191.85	$1,191.90