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	$118.84	12.181%	$133.3159	$133.32	$133.30	$133.30
Purchase #2	$129.43	4.166%	$134.8221	$134.82	$134.80	$134.80
Purchase #3	$144.87	5.329%	$152.5901	$152.59	$152.60	$152.60
Purchase #4	$174.69	9.579%	$191.4236	$191.42	$191.40	$191.40
Purchase #5	$160.81	10.753%	$178.1019	$178.10	$178.10	$178.10
Purchase #6	$78.73	8.579%	$85.4842	$85.48	$85.50	$85.50
Purchase #7	$12.84	10.766%	$14.2224	$14.22	$14.20	$14.20
7 purchase totals =	$820.21		$889.9602	$889.95	$889.90	$889.90