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	$92.64	8.316%	$100.3439	$100.34	$100.35	$100.30
Purchase #2	$150.52	10.468%	$166.2764	$166.28	$166.30	$166.30
Purchase #3	$79.55	12.790%	$89.7244	$89.72	$89.70	$89.70
Purchase #4	$7.42	12.278%	$8.331	$8.33	$8.35	$8.30
Purchase #5	$131.25	8.223%	$142.0427	$142.04	$142.05	$142.00
Purchase #6	$58.90	7.284%	$63.1903	$63.19	$63.20	$63.20
Purchase #7	$100.28	7.602%	$107.9033	$107.90	$107.90	$107.90
7 purchase totals =	$620.56		$677.8120	$677.80	$677.85	$677.70