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	$23.75	3.414%	$24.5608	$24.56	$24.55	$24.60
Purchase #2	$123.44	6.462%	$131.4167	$131.42	$131.40	$131.40
Purchase #3	$90.71	8.555%	$98.4702	$98.47	$98.45	$98.50
Purchase #4	$25.65	8.251%	$27.7664	$27.77	$27.75	$27.80
Purchase #5	$96.65	3.251%	$99.7921	$99.79	$99.80	$99.80
Purchase #6	$200.48	7.375%	$215.2654	$215.27	$215.25	$215.30
Purchase #7	$82.78	4.421%	$86.4397	$86.44	$86.45	$86.40
7 purchase totals =	$643.46		$683.7113	$683.72	$683.65	$683.80