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	$21.42	5.675%	$22.6356	$22.64	$22.65	$22.60
Purchase #2	$98.28	11.281%	$109.367	$109.37	$109.35	$109.40
Purchase #3	$92.57	13.791%	$105.3363	$105.34	$105.35	$105.30
Purchase #4	$238.38	7.161%	$255.4504	$255.45	$255.45	$255.50
Purchase #5	$139.80	7.637%	$150.4765	$150.48	$150.50	$150.50
Purchase #6	$43.44	9.506%	$47.5694	$47.57	$47.55	$47.60
Purchase #7	$125.79	9.828%	$138.1526	$138.15	$138.15	$138.20
7 purchase totals =	$759.68		$828.9878	$829.00	$829.00	$829.10