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	$174.25	12.759%	$196.4826	$196.48	$196.50	$196.50
Purchase #2	$237.26	9.755%	$260.4047	$260.40	$260.40	$260.40
Purchase #3	$156.35	3.707%	$162.1459	$162.15	$162.15	$162.10
Purchase #4	$205.41	7.592%	$221.0047	$221.00	$221.00	$221.00
Purchase #5	$222.71	8.872%	$242.4688	$242.47	$242.45	$242.50
Purchase #6	$50.86	7.567%	$54.7086	$54.71	$54.70	$54.70
Purchase #7	$163.88	11.864%	$183.3227	$183.32	$183.30	$183.30
7 purchase totals =	$1,210.72		$1,320.5380	$1,320.53	$1,320.50	$1,320.50