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	$84.94	6.565%	$90.5163	$90.52	$90.50	$90.50
Purchase #2	$239.63	4.496%	$250.4038	$250.40	$250.40	$250.40
Purchase #3	$129.78	9.159%	$141.6666	$141.67	$141.65	$141.70
Purchase #4	$86.78	4.219%	$90.4412	$90.44	$90.45	$90.40
Purchase #5	$239.87	11.701%	$267.9372	$267.94	$267.95	$267.90
Purchase #6	$94.58	6.102%	$100.3513	$100.35	$100.35	$100.40
Purchase #7	$110.86	10.184%	$122.15	$122.15	$122.15	$122.20
7 purchase totals =	$986.44		$1,063.4664	$1,063.47	$1,063.45	$1,063.50