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	$104.87	10.709%	$116.1005	$116.10	$116.10	$116.10
Purchase #2	$156.94	3.572%	$162.5459	$162.55	$162.55	$162.50
Purchase #3	$170.84	10.622%	$188.9866	$188.99	$189.00	$189.00
Purchase #4	$24.55	11.299%	$27.3239	$27.32	$27.30	$27.30
Purchase #5	$38.60	5.496%	$40.7215	$40.72	$40.70	$40.70
Purchase #6	$146.44	3.811%	$152.0208	$152.02	$152.00	$152.00
Purchase #7	$151.27	6.196%	$160.6427	$160.64	$160.65	$160.60
7 purchase totals =	$793.51		$848.3419	$848.34	$848.30	$848.20