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	$89.34	12.453%	$100.4655	$100.47	$100.45	$100.50
Purchase #2	$119.54	5.216%	$125.7752	$125.78	$125.80	$125.80
Purchase #3	$130.86	6.870%	$139.8501	$139.85	$139.85	$139.90
Purchase #4	$130.55	6.873%	$139.5227	$139.52	$139.50	$139.50
Purchase #5	$48.60	12.397%	$54.6249	$54.62	$54.60	$54.60
Purchase #6	$130.53	5.790%	$138.0877	$138.09	$138.10	$138.10
Purchase #7	$133.57	7.527%	$143.6238	$143.62	$143.60	$143.60
7 purchase totals =	$782.99		$841.9499	$841.95	$841.90	$842.00