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	$136.67	5.350%	$143.9818	$143.98	$144.00	$144.00
Purchase #2	$104.88	5.806%	$110.9693	$110.97	$110.95	$111.00
Purchase #3	$183.90	8.446%	$199.4322	$199.43	$199.45	$199.40
Purchase #4	$137.34	9.608%	$150.5356	$150.54	$150.55	$150.50
Purchase #5	$70.45	11.713%	$78.7018	$78.70	$78.70	$78.70
Purchase #6	$55.59	7.628%	$59.8304	$59.83	$59.85	$59.80
Purchase #7	$33.79	12.872%	$38.1394	$38.14	$38.15	$38.10
7 purchase totals =	$722.62		$781.5905	$781.59	$781.65	$781.50