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	$12.31	8.757%	$13.388	$13.39	$13.40	$13.40
Purchase #2	$186.37	7.570%	$200.4782	$200.48	$200.50	$200.50
Purchase #3	$208.61	7.214%	$223.6591	$223.66	$223.65	$223.70
Purchase #4	$45.54	13.214%	$51.5577	$51.56	$51.55	$51.60
Purchase #5	$122.93	4.225%	$128.1238	$128.12	$128.10	$128.10
Purchase #6	$122.93	13.791%	$139.8833	$139.88	$139.90	$139.90
Purchase #7	$244.27	8.329%	$264.6152	$264.62	$264.60	$264.60
7 purchase totals =	$942.96		$1,021.7053	$1,021.71	$1,021.70	$1,021.80