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	$238.30	4.850%	$249.8576	$249.86	$249.85	$249.90
Purchase #2	$238.93	9.710%	$262.1301	$262.13	$262.15	$262.10
Purchase #3	$96.84	7.237%	$103.8483	$103.85	$103.85	$103.80
Purchase #4	$17.62	5.284%	$18.551	$18.55	$18.55	$18.60
Purchase #5	$19.34	3.597%	$20.0357	$20.04	$20.05	$20.00
Purchase #6	$249.56	13.368%	$282.9212	$282.92	$282.90	$282.90
Purchase #7	$195.97	7.133%	$209.9485	$209.95	$209.95	$209.90
7 purchase totals =	$1,056.56		$1,147.2924	$1,147.30	$1,147.30	$1,147.20