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	$80.92	12.114%	$90.7226	$90.72	$90.70	$90.70
Purchase #2	$102.59	3.165%	$105.837	$105.84	$105.85	$105.80
Purchase #3	$174.67	4.606%	$182.7153	$182.72	$182.70	$182.70
Purchase #4	$162.41	3.694%	$168.4094	$168.41	$168.40	$168.40
Purchase #5	$227.44	3.227%	$234.7795	$234.78	$234.80	$234.80
Purchase #6	$151.99	6.598%	$162.0183	$162.02	$162.00	$162.00
Purchase #7	$131.67	5.250%	$138.5827	$138.58	$138.60	$138.60
7 purchase totals =	$1,031.69		$1,083.0648	$1,083.07	$1,083.05	$1,083.00