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	$16.56	11.750%	$18.5058	$18.51	$18.50	$18.50
Purchase #2	$47.89	6.438%	$50.9732	$50.97	$50.95	$51.00
Purchase #3	$82.73	11.377%	$92.1422	$92.14	$92.15	$92.10
Purchase #4	$41.66	9.358%	$45.5585	$45.56	$45.55	$45.60
Purchase #5	$11.71	6.135%	$12.4284	$12.43	$12.45	$12.40
Purchase #6	$211.48	5.115%	$222.2972	$222.30	$222.30	$222.30
Purchase #7	$138.89	9.679%	$152.3332	$152.33	$152.35	$152.30
7 purchase totals =	$550.92		$594.2385	$594.24	$594.25	$594.20