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	$143.87	6.198%	$152.7871	$152.79	$152.80	$152.80
Purchase #2	$228.39	8.840%	$248.5797	$248.58	$248.60	$248.60
Purchase #3	$74.86	12.851%	$84.4803	$84.48	$84.50	$84.50
Purchase #4	$178.88	9.741%	$196.3047	$196.30	$196.30	$196.30
Purchase #5	$28.88	11.679%	$32.2529	$32.25	$32.25	$32.30
Purchase #6	$78.82	8.274%	$85.3416	$85.34	$85.35	$85.30
Purchase #7	$94.32	9.174%	$102.9729	$102.97	$102.95	$103.00
7 purchase totals =	$828.02		$902.7192	$902.71	$902.75	$902.80