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	$86.49	13.318%	$98.0087	$98.01	$98.00	$98.00
Purchase #2	$18.80	7.826%	$20.2713	$20.27	$20.25	$20.30
Purchase #3	$48.74	4.604%	$50.984	$50.98	$51.00	$51.00
Purchase #4	$37.59	13.837%	$42.7913	$42.79	$42.80	$42.80
Purchase #5	$27.59	10.428%	$30.4671	$30.47	$30.45	$30.50
Purchase #6	$185.59	12.513%	$208.8129	$208.81	$208.80	$208.80
Purchase #7	$133.51	10.750%	$147.8623	$147.86	$147.85	$147.90
7 purchase totals =	$538.31		$599.1976	$599.19	$599.15	$599.30