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	$35.83	10.769%	$39.6885	$39.69	$39.70	$39.70
Purchase #2	$52.83	12.810%	$59.5975	$59.60	$59.60	$59.60
Purchase #3	$92.69	5.428%	$97.7212	$97.72	$97.70	$97.70
Purchase #4	$188.48	11.731%	$210.5906	$210.59	$210.60	$210.60
Purchase #5	$244.49	6.526%	$260.4454	$260.45	$260.45	$260.40
Purchase #6	$103.58	3.623%	$107.3327	$107.33	$107.35	$107.30
Purchase #7	$146.34	6.584%	$155.975	$155.98	$156.00	$156.00
7 purchase totals =	$864.24		$931.3509	$931.36	$931.40	$931.30