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	$33.78	3.603%	$34.9971	$35.00	$35.00	$35.00
Purchase #2	$115.84	6.513%	$123.3847	$123.38	$123.40	$123.40
Purchase #3	$82.33	5.550%	$86.8993	$86.90	$86.90	$86.90
Purchase #4	$145.27	3.593%	$150.4896	$150.49	$150.50	$150.50
Purchase #5	$102.68	5.614%	$108.4445	$108.44	$108.45	$108.40
Purchase #6	$21.93	6.826%	$23.4269	$23.43	$23.45	$23.40
Purchase #7	$39.91	13.667%	$45.3645	$45.36	$45.35	$45.40
7 purchase totals =	$541.74		$573.0066	$573.00	$573.05	$573.00