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	$153.78	8.342%	$166.6083	$166.61	$166.60	$166.60
Purchase #2	$231.72	10.111%	$255.1492	$255.15	$255.15	$255.10
Purchase #3	$118.70	9.573%	$130.0632	$130.06	$130.05	$130.10
Purchase #4	$243.52	8.815%	$264.9863	$264.99	$265.00	$265.00
Purchase #5	$73.83	10.305%	$81.4382	$81.44	$81.45	$81.40
Purchase #6	$7.42	5.700%	$7.8429	$7.84	$7.85	$7.80
Purchase #7	$27.47	5.271%	$28.9179	$28.92	$28.90	$28.90
7 purchase totals =	$856.44		$935.0060	$935.01	$935.00	$934.90