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	$70.64	10.535%	$78.0819	$78.08	$78.10	$78.10
Purchase #2	$206.39	13.762%	$234.7934	$234.79	$234.80	$234.80
Purchase #3	$72.41	9.837%	$79.533	$79.53	$79.55	$79.50
Purchase #4	$34.73	6.649%	$37.0392	$37.04	$37.05	$37.00
Purchase #5	$173.70	7.607%	$186.9134	$186.91	$186.90	$186.90
Purchase #6	$84.83	7.120%	$90.8699	$90.87	$90.85	$90.90
Purchase #7	$156.92	5.385%	$165.3701	$165.37	$165.35	$165.40
7 purchase totals =	$799.62		$872.6009	$872.59	$872.60	$872.60