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	$53.33	6.522%	$56.8082	$56.81	$56.80	$56.80
Purchase #2	$67.98	5.807%	$71.9276	$71.93	$71.95	$71.90
Purchase #3	$17.85	3.830%	$18.5337	$18.53	$18.55	$18.50
Purchase #4	$160.32	5.317%	$168.8442	$168.84	$168.85	$168.80
Purchase #5	$139.46	5.338%	$146.9044	$146.90	$146.90	$146.90
Purchase #6	$61.69	13.428%	$69.9737	$69.97	$69.95	$70.00
Purchase #7	$90.99	8.660%	$98.8697	$98.87	$98.85	$98.90
7 purchase totals =	$591.62		$631.8615	$631.85	$631.85	$631.80