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	$79.26	4.449%	$82.7863	$82.79	$82.80	$82.80
Purchase #2	$129.91	10.517%	$143.5726	$143.57	$143.55	$143.60
Purchase #3	$117.73	9.481%	$128.892	$128.89	$128.90	$128.90
Purchase #4	$177.43	4.539%	$185.4835	$185.48	$185.50	$185.50
Purchase #5	$170.90	9.844%	$187.7234	$187.72	$187.70	$187.70
Purchase #6	$128.45	13.142%	$145.3309	$145.33	$145.35	$145.30
Purchase #7	$23.77	3.534%	$24.61	$24.61	$24.60	$24.60
7 purchase totals =	$827.45		$898.3987	$898.39	$898.40	$898.40