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	$231.51	5.197%	$243.5416	$243.54	$243.55	$243.50
Purchase #2	$46.57	6.177%	$49.4466	$49.45	$49.45	$49.40
Purchase #3	$179.97	5.264%	$189.4436	$189.44	$189.45	$189.40
Purchase #4	$65.62	12.399%	$73.7562	$73.76	$73.75	$73.80
Purchase #5	$82.38	9.509%	$90.2135	$90.21	$90.20	$90.20
Purchase #6	$42.36	3.381%	$43.7922	$43.79	$43.80	$43.80
Purchase #7	$136.32	10.673%	$150.8694	$150.87	$150.85	$150.90
7 purchase totals =	$784.73		$841.0631	$841.06	$841.05	$841.00