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	$244.41	4.383%	$255.1225	$255.12	$255.10	$255.10
Purchase #2	$196.91	9.385%	$215.39	$215.39	$215.40	$215.40
Purchase #3	$163.48	10.828%	$181.1816	$181.18	$181.20	$181.20
Purchase #4	$220.70	11.166%	$245.3434	$245.34	$245.35	$245.30
Purchase #5	$83.43	9.654%	$91.4843	$91.48	$91.50	$91.50
Purchase #6	$60.81	3.495%	$62.9353	$62.94	$62.95	$62.90
Purchase #7	$141.89	11.172%	$157.742	$157.74	$157.75	$157.70
7 purchase totals =	$1,111.63		$1,209.1991	$1,209.19	$1,209.25	$1,209.10