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	$142.78	8.183%	$154.4637	$154.46	$154.45	$154.50
Purchase #2	$59.69	13.616%	$67.8174	$67.82	$67.80	$67.80
Purchase #3	$51.35	4.182%	$53.4975	$53.50	$53.50	$53.50
Purchase #4	$165.27	7.648%	$177.9098	$177.91	$177.90	$177.90
Purchase #5	$108.38	3.720%	$112.4117	$112.41	$112.40	$112.40
Purchase #6	$230.82	8.528%	$250.5043	$250.50	$250.50	$250.50
Purchase #7	$166.86	8.333%	$180.7644	$180.76	$180.75	$180.80
7 purchase totals =	$925.15		$997.3688	$997.36	$997.30	$997.40