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	$90.81	6.642%	$96.8416	$96.84	$96.85	$96.80
Purchase #2	$184.49	3.223%	$190.4361	$190.44	$190.45	$190.40
Purchase #3	$111.60	10.840%	$123.6974	$123.70	$123.70	$123.70
Purchase #4	$153.99	8.231%	$166.6649	$166.66	$166.65	$166.70
Purchase #5	$201.66	8.836%	$219.4787	$219.48	$219.50	$219.50
Purchase #6	$112.46	7.333%	$120.7067	$120.71	$120.70	$120.70
Purchase #7	$81.47	5.591%	$86.025	$86.03	$86.05	$86.00
7 purchase totals =	$936.48		$1,003.8504	$1,003.86	$1,003.90	$1,003.80