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	$156.89	4.822%	$164.4552	$164.46	$164.45	$164.50
Purchase #2	$125.89	13.198%	$142.505	$142.51	$142.50	$142.50
Purchase #3	$90.68	4.535%	$94.7923	$94.79	$94.80	$94.80
Purchase #4	$130.28	6.278%	$138.459	$138.46	$138.45	$138.50
Purchase #5	$20.98	5.797%	$22.1962	$22.20	$22.20	$22.20
Purchase #6	$225.96	7.773%	$243.5239	$243.52	$243.50	$243.50
Purchase #7	$69.93	8.785%	$76.0734	$76.07	$76.05	$76.10
7 purchase totals =	$820.61		$882.0050	$882.01	$881.95	$882.10