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	$133.63	8.696%	$145.2505	$145.25	$145.25	$145.30
Purchase #2	$245.51	4.516%	$256.5972	$256.60	$256.60	$256.60
Purchase #3	$23.83	8.659%	$25.8934	$25.89	$25.90	$25.90
Purchase #4	$159.25	13.320%	$180.4621	$180.46	$180.45	$180.50
Purchase #5	$156.38	5.857%	$165.5392	$165.54	$165.55	$165.50
Purchase #6	$133.64	10.260%	$147.3515	$147.35	$147.35	$147.40
Purchase #7	$54.88	7.829%	$59.1766	$59.18	$59.20	$59.20
7 purchase totals =	$907.12		$980.2705	$980.27	$980.30	$980.40