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	$131.45	9.687%	$144.1836	$144.18	$144.20	$144.20
Purchase #2	$189.61	8.116%	$204.9987	$205.00	$205.00	$205.00
Purchase #3	$125.31	12.418%	$140.871	$140.87	$140.85	$140.90
Purchase #4	$95.90	7.489%	$103.082	$103.08	$103.10	$103.10
Purchase #5	$155.33	12.749%	$175.133	$175.13	$175.15	$175.10
Purchase #6	$178.27	6.797%	$190.387	$190.39	$190.40	$190.40
Purchase #7	$39.72	12.174%	$44.5555	$44.56	$44.55	$44.60
7 purchase totals =	$915.59		$1,003.2108	$1,003.21	$1,003.25	$1,003.30