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	$71.42	13.308%	$80.9246	$80.92	$80.90	$80.90
Purchase #2	$43.64	8.204%	$47.2202	$47.22	$47.20	$47.20
Purchase #3	$243.36	5.376%	$256.443	$256.44	$256.45	$256.40
Purchase #4	$74.78	6.243%	$79.4485	$79.45	$79.45	$79.40
Purchase #5	$237.74	7.529%	$255.6394	$255.64	$255.65	$255.60
Purchase #6	$158.48	12.809%	$178.7797	$178.78	$178.80	$178.80
Purchase #7	$224.81	3.564%	$232.8222	$232.82	$232.80	$232.80
7 purchase totals =	$1,054.23		$1,131.2776	$1,131.27	$1,131.25	$1,131.10