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	$45.27	10.639%	$50.0863	$50.09	$50.10	$50.10
Purchase #2	$109.45	3.701%	$113.5007	$113.50	$113.50	$113.50
Purchase #3	$180.45	9.293%	$197.2192	$197.22	$197.20	$197.20
Purchase #4	$124.77	12.697%	$140.612	$140.61	$140.60	$140.60
Purchase #5	$57.77	3.376%	$59.7203	$59.72	$59.70	$59.70
Purchase #6	$147.28	5.543%	$155.4437	$155.44	$155.45	$155.40
Purchase #7	$70.47	4.151%	$73.3952	$73.40	$73.40	$73.40
7 purchase totals =	$735.46		$789.9774	$789.98	$789.95	$789.90