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	$22.93	6.229%	$24.3583	$24.36	$24.35	$24.40
Purchase #2	$131.72	6.210%	$139.8998	$139.90	$139.90	$139.90
Purchase #3	$35.49	5.426%	$37.4157	$37.42	$37.40	$37.40
Purchase #4	$178.59	7.764%	$192.4557	$192.46	$192.45	$192.50
Purchase #5	$245.26	6.332%	$260.7899	$260.79	$260.80	$260.80
Purchase #6	$46.63	7.228%	$50.0004	$50.00	$50.00	$50.00
Purchase #7	$121.61	4.781%	$127.4242	$127.42	$127.40	$127.40
7 purchase totals =	$782.23		$832.3440	$832.35	$832.30	$832.40