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	$99.62	13.703%	$113.2709	$113.27	$113.25	$113.30
Purchase #2	$55.81	6.479%	$59.4259	$59.43	$59.45	$59.40
Purchase #3	$171.91	8.687%	$186.8438	$186.84	$186.85	$186.80
Purchase #4	$236.32	6.601%	$251.9195	$251.92	$251.90	$251.90
Purchase #5	$195.55	12.432%	$219.8608	$219.86	$219.85	$219.90
Purchase #6	$87.27	4.594%	$91.2792	$91.28	$91.30	$91.30
Purchase #7	$61.60	4.296%	$64.2463	$64.25	$64.25	$64.20
7 purchase totals =	$908.08		$986.8464	$986.85	$986.85	$986.80