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	$34.95	9.700%	$38.3402	$38.34	$38.35	$38.30
Purchase #2	$167.43	7.423%	$179.8583	$179.86	$179.85	$179.90
Purchase #3	$135.38	5.250%	$142.4875	$142.49	$142.50	$142.50
Purchase #4	$75.40	4.717%	$78.9566	$78.96	$78.95	$79.00
Purchase #5	$116.73	12.144%	$130.9057	$130.91	$130.90	$130.90
Purchase #6	$103.62	5.634%	$109.458	$109.46	$109.45	$109.50
Purchase #7	$120.65	11.294%	$134.2762	$134.28	$134.30	$134.30
7 purchase totals =	$754.16		$814.2825	$814.30	$814.30	$814.40