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	$98.33	7.293%	$105.5012	$105.50	$105.50	$105.50
Purchase #2	$245.33	9.249%	$268.0206	$268.02	$268.00	$268.00
Purchase #3	$230.72	13.576%	$262.0425	$262.04	$262.05	$262.00
Purchase #4	$78.42	11.163%	$87.174	$87.17	$87.15	$87.20
Purchase #5	$174.61	6.105%	$185.2699	$185.27	$185.25	$185.30
Purchase #6	$76.50	13.536%	$86.855	$86.86	$86.85	$86.90
Purchase #7	$133.79	11.453%	$149.113	$149.11	$149.10	$149.10
7 purchase totals =	$1,037.70		$1,143.9762	$1,143.97	$1,143.90	$1,144.00