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	$42.82	11.658%	$47.812	$47.81	$47.80	$47.80
Purchase #2	$248.67	13.209%	$281.5168	$281.52	$281.50	$281.50
Purchase #3	$164.94	11.830%	$184.4524	$184.45	$184.45	$184.50
Purchase #4	$41.96	5.171%	$44.1298	$44.13	$44.15	$44.10
Purchase #5	$235.82	3.630%	$244.3803	$244.38	$244.40	$244.40
Purchase #6	$187.66	3.628%	$194.4683	$194.47	$194.45	$194.50
Purchase #7	$78.88	13.785%	$89.7536	$89.75	$89.75	$89.80
7 purchase totals =	$1,000.75		$1,086.5132	$1,086.51	$1,086.50	$1,086.60