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	$6.62	7.767%	$7.1342	$7.13	$7.15	$7.10
Purchase #2	$47.86	11.559%	$53.3921	$53.39	$53.40	$53.40
Purchase #3	$99.99	9.780%	$109.769	$109.77	$109.75	$109.80
Purchase #4	$104.49	11.595%	$116.6056	$116.61	$116.60	$116.60
Purchase #5	$236.33	3.756%	$245.2066	$245.21	$245.20	$245.20
Purchase #6	$181.34	4.805%	$190.0534	$190.05	$190.05	$190.10
Purchase #7	$166.69	11.650%	$186.1094	$186.11	$186.10	$186.10
7 purchase totals =	$843.32		$908.2703	$908.27	$908.25	$908.30