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	$57.34	4.452%	$59.8928	$59.89	$59.90	$59.90
Purchase #2	$20.29	4.212%	$21.1446	$21.14	$21.15	$21.10
Purchase #3	$160.82	8.215%	$174.0314	$174.03	$174.05	$174.00
Purchase #4	$92.48	13.418%	$104.889	$104.89	$104.90	$104.90
Purchase #5	$139.70	10.869%	$154.884	$154.88	$154.90	$154.90
Purchase #6	$100.49	13.285%	$113.8401	$113.84	$113.85	$113.80
Purchase #7	$209.57	4.302%	$218.5857	$218.59	$218.60	$218.60
7 purchase totals =	$780.69		$847.2676	$847.26	$847.35	$847.20