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	$118.69	13.793%	$135.0609	$135.06	$135.05	$135.10
Purchase #2	$70.65	3.635%	$73.2181	$73.22	$73.20	$73.20
Purchase #3	$224.74	13.849%	$255.8642	$255.86	$255.85	$255.90
Purchase #4	$200.88	7.432%	$215.8094	$215.81	$215.80	$215.80
Purchase #5	$158.33	9.364%	$173.156	$173.16	$173.15	$173.20
Purchase #6	$163.55	13.455%	$185.5557	$185.56	$185.55	$185.60
Purchase #7	$37.52	13.292%	$42.5072	$42.51	$42.50	$42.50
7 purchase totals =	$974.36		$1,081.1715	$1,081.18	$1,081.10	$1,081.30