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	$46.87	3.767%	$48.6356	$48.64	$48.65	$48.60
Purchase #2	$30.36	11.662%	$33.9006	$33.90	$33.90	$33.90
Purchase #3	$33.41	10.685%	$36.9799	$36.98	$37.00	$37.00
Purchase #4	$215.89	4.371%	$225.3266	$225.33	$225.35	$225.30
Purchase #5	$167.61	10.535%	$185.2677	$185.27	$185.25	$185.30
Purchase #6	$66.78	9.120%	$72.8703	$72.87	$72.85	$72.90
Purchase #7	$42.93	9.836%	$47.1526	$47.15	$47.15	$47.20
7 purchase totals =	$603.85		$650.1333	$650.14	$650.15	$650.20