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	$134.92	7.424%	$144.9365	$144.94	$144.95	$144.90
Purchase #2	$83.32	3.121%	$85.9204	$85.92	$85.90	$85.90
Purchase #3	$110.34	10.403%	$121.8187	$121.82	$121.80	$121.80
Purchase #4	$67.74	7.111%	$72.557	$72.56	$72.55	$72.60
Purchase #5	$16.29	6.845%	$17.4051	$17.41	$17.40	$17.40
Purchase #6	$159.30	5.214%	$167.6059	$167.61	$167.60	$167.60
Purchase #7	$75.91	3.600%	$78.6428	$78.64	$78.65	$78.60
7 purchase totals =	$647.82		$688.8864	$688.90	$688.85	$688.80