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	$51.66	8.358%	$55.9777	$55.98	$56.00	$56.00
Purchase #2	$42.97	7.618%	$46.2435	$46.24	$46.25	$46.20
Purchase #3	$55.34	8.359%	$59.9659	$59.97	$59.95	$60.00
Purchase #4	$81.59	4.637%	$85.3733	$85.37	$85.35	$85.40
Purchase #5	$102.96	6.320%	$109.4671	$109.47	$109.45	$109.50
Purchase #6	$181.38	7.461%	$194.9128	$194.91	$194.90	$194.90
Purchase #7	$105.64	7.386%	$113.4426	$113.44	$113.45	$113.40
7 purchase totals =	$621.54		$665.3829	$665.38	$665.35	$665.40