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	$46.90	13.606%	$53.2812	$53.28	$53.30	$53.30
Purchase #2	$70.44	11.242%	$78.3589	$78.36	$78.35	$78.40
Purchase #3	$87.71	11.208%	$97.5405	$97.54	$97.55	$97.50
Purchase #4	$229.89	3.715%	$238.4304	$238.43	$238.45	$238.40
Purchase #5	$170.75	6.169%	$181.2836	$181.28	$181.30	$181.30
Purchase #6	$208.90	13.801%	$237.7303	$237.73	$237.75	$237.70
Purchase #7	$12.70	5.397%	$13.3854	$13.39	$13.40	$13.40
7 purchase totals =	$827.29		$900.0103	$900.01	$900.10	$900.00