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	$54.68	8.495%	$59.3251	$59.33	$59.35	$59.30
Purchase #2	$37.58	8.799%	$40.8867	$40.89	$40.90	$40.90
Purchase #3	$179.98	4.567%	$188.1997	$188.20	$188.20	$188.20
Purchase #4	$122.54	4.221%	$127.7124	$127.71	$127.70	$127.70
Purchase #5	$137.84	3.421%	$142.5555	$142.56	$142.55	$142.60
Purchase #6	$108.99	6.765%	$116.3632	$116.36	$116.35	$116.40
Purchase #7	$84.72	9.376%	$92.6633	$92.66	$92.65	$92.70
7 purchase totals =	$726.33		$767.7059	$767.71	$767.70	$767.80