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	$85.79	5.512%	$90.5187	$90.52	$90.50	$90.50
Purchase #2	$11.66	11.853%	$13.0421	$13.04	$13.05	$13.00
Purchase #3	$249.25	10.791%	$276.1466	$276.15	$276.15	$276.10
Purchase #4	$62.52	3.678%	$64.8195	$64.82	$64.80	$64.80
Purchase #5	$124.85	11.452%	$139.1478	$139.15	$139.15	$139.10
Purchase #6	$164.30	7.425%	$176.4993	$176.50	$176.50	$176.50
Purchase #7	$109.78	3.573%	$113.7024	$113.70	$113.70	$113.70
7 purchase totals =	$808.15		$873.8764	$873.88	$873.85	$873.70