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	$134.53	4.650%	$140.7856	$140.79	$140.80	$140.80
Purchase #2	$210.52	13.111%	$238.1213	$238.12	$238.10	$238.10
Purchase #3	$241.40	13.594%	$274.2159	$274.22	$274.20	$274.20
Purchase #4	$220.47	11.159%	$245.0722	$245.07	$245.05	$245.10
Purchase #5	$34.94	7.585%	$37.5902	$37.59	$37.60	$37.60
Purchase #6	$31.89	7.662%	$34.3334	$34.33	$34.35	$34.30
Purchase #7	$29.59	4.705%	$30.9822	$30.98	$31.00	$31.00
7 purchase totals =	$903.34		$1,001.1008	$1,001.10	$1,001.10	$1,001.10