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	$59.67	12.501%	$67.1293	$67.13	$67.15	$67.10
Purchase #2	$180.36	3.394%	$186.4814	$186.48	$186.50	$186.50
Purchase #3	$86.96	12.727%	$98.0274	$98.03	$98.05	$98.00
Purchase #4	$241.76	3.275%	$249.6776	$249.68	$249.70	$249.70
Purchase #5	$50.43	9.575%	$55.2587	$55.26	$55.25	$55.30
Purchase #6	$69.39	10.398%	$76.6052	$76.61	$76.60	$76.60
Purchase #7	$40.89	12.203%	$45.8798	$45.88	$45.90	$45.90
7 purchase totals =	$729.46		$779.0594	$779.07	$779.15	$779.10