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	$90.56	10.507%	$100.0751	$100.08	$100.10	$100.10
Purchase #2	$79.54	3.248%	$82.1235	$82.12	$82.10	$82.10
Purchase #3	$41.59	13.183%	$47.0728	$47.07	$47.05	$47.10
Purchase #4	$115.59	4.334%	$120.5997	$120.60	$120.60	$120.60
Purchase #5	$75.68	10.198%	$83.3978	$83.40	$83.40	$83.40
Purchase #6	$238.73	7.647%	$256.9857	$256.99	$257.00	$257.00
Purchase #7	$229.69	11.276%	$255.5898	$255.59	$255.60	$255.60
7 purchase totals =	$871.38		$945.8444	$945.85	$945.85	$945.90