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	$39.55	4.636%	$41.3835	$41.38	$41.40	$41.40
Purchase #2	$169.86	9.260%	$185.589	$185.59	$185.60	$185.60
Purchase #3	$129.33	6.574%	$137.8322	$137.83	$137.85	$137.80
Purchase #4	$216.68	11.737%	$242.1117	$242.11	$242.10	$242.10
Purchase #5	$161.57	7.331%	$173.4147	$173.41	$173.40	$173.40
Purchase #6	$248.25	12.731%	$279.8547	$279.85	$279.85	$279.90
Purchase #7	$82.83	8.683%	$90.0221	$90.02	$90.00	$90.00
7 purchase totals =	$1,048.07		$1,150.2079	$1,150.19	$1,150.20	$1,150.20