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	$116.66	10.367%	$128.7541	$128.75	$128.75	$128.80
Purchase #2	$147.97	11.665%	$165.2307	$165.23	$165.25	$165.20
Purchase #3	$137.70	4.700%	$144.1719	$144.17	$144.15	$144.20
Purchase #4	$136.65	11.818%	$152.7993	$152.80	$152.80	$152.80
Purchase #5	$160.79	11.866%	$179.8693	$179.87	$179.85	$179.90
Purchase #6	$73.71	12.236%	$82.7292	$82.73	$82.75	$82.70
Purchase #7	$106.96	10.789%	$118.4999	$118.50	$118.50	$118.50
7 purchase totals =	$880.44		$972.0544	$972.05	$972.05	$972.10