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	$133.74	3.141%	$137.9408	$137.94	$137.95	$137.90
Purchase #2	$111.38	8.238%	$120.5555	$120.56	$120.55	$120.60
Purchase #3	$12.66	10.421%	$13.9793	$13.98	$14.00	$14.00
Purchase #4	$94.91	5.793%	$100.4081	$100.41	$100.40	$100.40
Purchase #5	$126.37	5.795%	$133.6931	$133.69	$133.70	$133.70
Purchase #6	$58.39	7.285%	$62.6437	$62.64	$62.65	$62.60
Purchase #7	$18.89	10.871%	$20.9435	$20.94	$20.95	$20.90
7 purchase totals =	$556.34		$590.1640	$590.16	$590.20	$590.10