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	$74.49	5.181%	$78.3493	$78.35	$78.35	$78.30
Purchase #2	$79.25	4.543%	$82.8503	$82.85	$82.85	$82.90
Purchase #3	$143.33	9.818%	$157.4021	$157.40	$157.40	$157.40
Purchase #4	$185.94	6.840%	$198.6583	$198.66	$198.65	$198.70
Purchase #5	$38.88	3.387%	$40.1969	$40.20	$40.20	$40.20
Purchase #6	$195.89	6.849%	$209.3065	$209.31	$209.30	$209.30
Purchase #7	$241.52	13.482%	$274.0817	$274.08	$274.10	$274.10
7 purchase totals =	$959.30		$1,040.8451	$1,040.85	$1,040.85	$1,040.90