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	$37.83	11.273%	$42.0946	$42.09	$42.10	$42.10
Purchase #2	$27.92	10.596%	$30.8784	$30.88	$30.90	$30.90
Purchase #3	$166.36	12.291%	$186.8073	$186.81	$186.80	$186.80
Purchase #4	$39.71	7.451%	$42.6688	$42.67	$42.65	$42.70
Purchase #5	$219.31	8.174%	$237.2364	$237.24	$237.25	$237.20
Purchase #6	$149.80	3.314%	$154.7644	$154.76	$154.75	$154.80
Purchase #7	$52.87	12.317%	$59.382	$59.38	$59.40	$59.40
7 purchase totals =	$693.80		$753.8319	$753.83	$753.85	$753.90