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	$21.32	7.383%	$22.8941	$22.89	$22.90	$22.90
Purchase #2	$249.43	12.123%	$279.6684	$279.67	$279.65	$279.70
Purchase #3	$117.93	4.837%	$123.6343	$123.63	$123.65	$123.60
Purchase #4	$152.98	11.522%	$170.6064	$170.61	$170.60	$170.60
Purchase #5	$19.31	3.199%	$19.9277	$19.93	$19.95	$19.90
Purchase #6	$112.85	9.357%	$123.4094	$123.41	$123.40	$123.40
Purchase #7	$59.44	5.821%	$62.9	$62.90	$62.90	$62.90
7 purchase totals =	$733.26		$803.0403	$803.04	$803.05	$803.00