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	$75.89	12.381%	$85.2859	$85.29	$85.30	$85.30
Purchase #2	$91.37	5.369%	$96.2757	$96.28	$96.30	$96.30
Purchase #3	$241.82	10.745%	$267.8036	$267.80	$267.80	$267.80
Purchase #4	$13.90	6.854%	$14.8527	$14.85	$14.85	$14.90
Purchase #5	$115.44	13.565%	$131.0994	$131.10	$131.10	$131.10
Purchase #6	$98.39	5.802%	$104.0986	$104.10	$104.10	$104.10
Purchase #7	$235.93	8.462%	$255.8944	$255.89	$255.90	$255.90
7 purchase totals =	$872.74		$955.3103	$955.31	$955.35	$955.40