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	$25.58	8.238%	$27.6873	$27.69	$27.70	$27.70
Purchase #2	$161.34	13.531%	$183.1709	$183.17	$183.15	$183.20
Purchase #3	$144.95	9.751%	$159.0841	$159.08	$159.10	$159.10
Purchase #4	$54.51	8.259%	$59.012	$59.01	$59.00	$59.00
Purchase #5	$225.27	9.832%	$247.4185	$247.42	$247.40	$247.40
Purchase #6	$219.94	3.676%	$228.025	$228.03	$228.05	$228.00
Purchase #7	$160.94	12.782%	$181.5114	$181.51	$181.50	$181.50
7 purchase totals =	$992.53		$1,085.9092	$1,085.91	$1,085.90	$1,085.90