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	$5.46	6.310%	$5.8045	$5.80	$5.80	$5.80
Purchase #2	$76.63	13.362%	$86.8693	$86.87	$86.85	$86.90
Purchase #3	$52.43	11.271%	$58.3394	$58.34	$58.35	$58.30
Purchase #4	$94.32	9.592%	$103.3672	$103.37	$103.35	$103.40
Purchase #5	$125.74	4.180%	$130.9959	$131.00	$131.00	$131.00
Purchase #6	$33.30	11.757%	$37.2151	$37.22	$37.20	$37.20
Purchase #7	$144.53	7.846%	$155.8698	$155.87	$155.85	$155.90
7 purchase totals =	$532.41		$578.4612	$578.47	$578.40	$578.50