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	$17.90	12.424%	$20.1239	$20.12	$20.10	$20.10
Purchase #2	$220.60	8.153%	$238.5855	$238.59	$238.60	$238.60
Purchase #3	$83.72	3.581%	$86.718	$86.72	$86.70	$86.70
Purchase #4	$65.61	13.305%	$74.3394	$74.34	$74.35	$74.30
Purchase #5	$70.85	10.254%	$78.115	$78.12	$78.10	$78.10
Purchase #6	$195.50	13.334%	$221.568	$221.57	$221.55	$221.60
Purchase #7	$223.99	7.650%	$241.1252	$241.13	$241.15	$241.10
7 purchase totals =	$878.17		$960.5750	$960.59	$960.55	$960.50