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	$160.42	11.267%	$178.4945	$178.49	$178.50	$178.50
Purchase #2	$92.53	6.549%	$98.5898	$98.59	$98.60	$98.60
Purchase #3	$84.39	6.793%	$90.1226	$90.12	$90.10	$90.10
Purchase #4	$183.39	3.569%	$189.9352	$189.94	$189.95	$189.90
Purchase #5	$196.28	6.351%	$208.7457	$208.75	$208.75	$208.70
Purchase #6	$27.57	4.617%	$28.8429	$28.84	$28.85	$28.80
Purchase #7	$226.52	8.554%	$245.8965	$245.90	$245.90	$245.90
7 purchase totals =	$971.10		$1,040.6272	$1,040.63	$1,040.65	$1,040.50