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	$186.45	12.322%	$209.4244	$209.42	$209.40	$209.40
Purchase #2	$111.47	10.500%	$123.1744	$123.17	$123.15	$123.20
Purchase #3	$91.28	5.747%	$96.5259	$96.53	$96.55	$96.50
Purchase #4	$55.71	11.325%	$62.0192	$62.02	$62.00	$62.00
Purchase #5	$49.85	8.370%	$54.0224	$54.02	$54.00	$54.00
Purchase #6	$75.96	3.595%	$78.6908	$78.69	$78.70	$78.70
Purchase #7	$123.31	4.721%	$129.1315	$129.13	$129.15	$129.10
7 purchase totals =	$694.03		$752.9886	$752.98	$752.95	$752.90