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	$61.70	9.428%	$67.5171	$67.52	$67.50	$67.50
Purchase #2	$95.67	13.826%	$108.8973	$108.90	$108.90	$108.90
Purchase #3	$77.70	11.244%	$86.4366	$86.44	$86.45	$86.40
Purchase #4	$125.80	8.354%	$136.3093	$136.31	$136.30	$136.30
Purchase #5	$72.40	8.118%	$78.2774	$78.28	$78.30	$78.30
Purchase #6	$144.73	3.775%	$150.1936	$150.19	$150.20	$150.20
Purchase #7	$47.74	12.504%	$53.7094	$53.71	$53.70	$53.70
7 purchase totals =	$625.74		$681.3407	$681.35	$681.35	$681.30