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	$35.33	10.374%	$38.9951	$39.00	$39.00	$39.00
Purchase #2	$59.59	3.404%	$61.6184	$61.62	$61.60	$61.60
Purchase #3	$74.44	5.732%	$78.7069	$78.71	$78.70	$78.70
Purchase #4	$167.88	11.300%	$186.8504	$186.85	$186.85	$186.90
Purchase #5	$94.66	12.364%	$106.3638	$106.36	$106.35	$106.40
Purchase #6	$184.27	8.791%	$200.4692	$200.47	$200.45	$200.50
Purchase #7	$153.62	5.553%	$162.1505	$162.15	$162.15	$162.20
7 purchase totals =	$769.79		$835.1543	$835.16	$835.10	$835.30