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	$89.26	5.523%	$94.1898	$94.19	$94.20	$94.20
Purchase #2	$126.59	12.523%	$142.4429	$142.44	$142.45	$142.40
Purchase #3	$43.85	4.127%	$45.6597	$45.66	$45.65	$45.70
Purchase #4	$142.36	3.814%	$147.7896	$147.79	$147.80	$147.80
Purchase #5	$10.40	8.233%	$11.2562	$11.26	$11.25	$11.30
Purchase #6	$36.45	7.272%	$39.1006	$39.10	$39.10	$39.10
Purchase #7	$55.74	7.406%	$59.8681	$59.87	$59.85	$59.90
7 purchase totals =	$504.65		$540.3069	$540.31	$540.30	$540.40