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	$199.65	12.352%	$224.3108	$224.31	$224.30	$224.30
Purchase #2	$61.70	5.558%	$65.1293	$65.13	$65.15	$65.10
Purchase #3	$144.59	5.727%	$152.8707	$152.87	$152.85	$152.90
Purchase #4	$205.31	7.834%	$221.394	$221.39	$221.40	$221.40
Purchase #5	$180.98	8.756%	$196.8266	$196.83	$196.85	$196.80
Purchase #6	$248.47	3.750%	$257.7876	$257.79	$257.80	$257.80
Purchase #7	$14.32	8.426%	$15.5266	$15.53	$15.55	$15.50
7 purchase totals =	$1,055.02		$1,133.8456	$1,133.85	$1,133.90	$1,133.80