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	$72.73	12.152%	$81.5681	$81.57	$81.55	$81.60
Purchase #2	$59.96	3.716%	$62.1881	$62.19	$62.20	$62.20
Purchase #3	$238.31	13.431%	$270.3174	$270.32	$270.30	$270.30
Purchase #4	$84.80	7.229%	$90.9302	$90.93	$90.95	$90.90
Purchase #5	$31.46	9.817%	$34.5484	$34.55	$34.55	$34.50
Purchase #6	$98.59	13.393%	$111.7942	$111.79	$111.80	$111.80
Purchase #7	$148.93	9.398%	$162.9264	$162.93	$162.95	$162.90
7 purchase totals =	$734.78		$814.2728	$814.28	$814.30	$814.20