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	$238.41	5.260%	$250.9504	$250.95	$250.95	$251.00
Purchase #2	$132.33	5.232%	$139.2535	$139.25	$139.25	$139.30
Purchase #3	$25.40	8.637%	$27.5938	$27.59	$27.60	$27.60
Purchase #4	$11.91	9.802%	$13.0774	$13.08	$13.10	$13.10
Purchase #5	$230.51	5.833%	$243.9556	$243.96	$243.95	$244.00
Purchase #6	$39.79	6.581%	$42.4086	$42.41	$42.40	$42.40
Purchase #7	$105.43	8.592%	$114.4885	$114.49	$114.50	$114.50
7 purchase totals =	$783.78		$831.7278	$831.73	$831.75	$831.90