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	$126.73	3.784%	$131.5255	$131.53	$131.55	$131.50
Purchase #2	$152.82	10.603%	$169.0235	$169.02	$169.00	$169.00
Purchase #3	$203.47	11.593%	$227.0583	$227.06	$227.05	$227.10
Purchase #4	$202.73	5.706%	$214.2978	$214.30	$214.30	$214.30
Purchase #5	$152.59	7.549%	$164.109	$164.11	$164.10	$164.10
Purchase #6	$9.95	8.801%	$10.8257	$10.83	$10.85	$10.80
Purchase #7	$95.86	9.171%	$104.6513	$104.65	$104.65	$104.70
7 purchase totals =	$944.15		$1,021.4911	$1,021.50	$1,021.50	$1,021.50